tests: use `--no-cache-dir` with `pip`

After 1a09563a615c, there's one more wheel that gets cached in the user's pip
cache in the macOS CI runner.  The wheel corresponds to the version being used
for the tests, but it doesn't get cached until the 3rd or 4th test shard is run,
so it's not an issue with installing to run the tests.  This seems to eliminate
that.

This doesn't seem to be an issue on Windows or Linux in my setup.  Windows not
being affected is likely because we set `$USERPROFILE` to redirect the home
directory to `$TESTTMP` when running tests, since 08fd76a553c9.  (When checking
with `"$PYTHON" -m pip cache dir`, it points to `$TESTTMP/pip/cache`.)  We do
also set `$HOME` to this same location when running posix tests, but I can't
tell what's going on locally in Linux, because running `pip` directly in the *.t
explodes, and `"$PYTHON" -m pip --version` prints `pip 9.0.1 from /usr/lib/python3/dist-packages`,
so that's likely before caching was enabled[1].  Running `python3.8 -m pip --version`
locally outside of the *.t (the same version used to invoke the test runner), prints
`pip 24.2 from /home/mharbison/.local/lib/python3.8/site-packages/pip (python 3.8)`.

In CI, both macOS and Linux print a modern version of `pip`, and list the cache
as being under `$TESTTMP`, but then it doesn't end up there on macOS.  No idea
if it is a pip bug, or what.  But let's be explict and disable caching.

[1] https://github.com/pypa/pip/blob/fe0925b3c00bf8956a0d33408df692ac364217d4/docs/html/topics/caching.md?plain=1#L37

tests/test-install.t

@@ -1,245 +1,245
   $ . "$RUNTESTDIR/helpers-testrepo.sh"
 
 hg debuginstall
   $ hg debuginstall
   checking encoding (ascii)...
   checking Python executable (*) (glob)
   checking Python implementation (*) (glob)
   checking Python version (3.*) (glob)
   checking Python lib (.*[Ll]ib.*)... (re) (no-pyoxidizer !)
   checking Python lib (.*pyoxidizer.*)... (re) (pyoxidizer !)
   checking Python security support (*) (glob)
     TLS 1.2 not supported by Python install; network connections lack modern security (?)
     SNI not supported by Python install; may have connectivity issues with some servers (?)
   checking Rust extensions \((installed|missing)\) (re)
   checking Mercurial version (*) (glob)
   checking Mercurial custom build (*) (glob)
   checking module policy (*) (glob)
   checking installed modules (*mercurial)... (glob) (no-pyoxidizer-in-memory !)
   checking installed modules (*/release/app/hg*)... (glob) (pyoxidizer-in-memory !)
   checking registered compression engines (*zlib*) (glob)
   checking available compression engines (*zlib*) (glob)
   checking available compression engines for wire protocol (*zlib*) (glob)
   checking "re2" regexp engine \((available|missing)\) (re)
   checking templates (*mercurial?templates)... (glob) (no-pyoxidizer !)
   checking templates (*app?templates)... (glob) (pyoxidizer !)
   checking default template (*mercurial?templates?map-cmdline.default) (glob) (no-pyoxidizer !)
   checking default template (*app?templates?map-cmdline.default) (glob) (pyoxidizer !)
   checking commit editor... (*) (glob)
   checking username (test)
   no problems detected
 
 hg debuginstall JSON
   $ hg debuginstall -Tjson | sed 's|\\\\|\\|g'
   [
    {
     "compengines": ["bz2", "bz2truncated", "none", "zlib"*], (glob)
     "compenginesavail": ["bz2", "bz2truncated", "none", "zlib"*], (glob)
     "compenginesserver": [*"zlib"*], (glob)
     "defaulttemplate": "*mercurial?templates?map-cmdline.default", (glob) (no-pyoxidizer !)
     "defaulttemplate": "*app?templates?map-cmdline.default", (glob) (pyoxidizer !)
     "defaulttemplateerror": null,
     "defaulttemplatenotfound": "default",
     "editor": "*", (glob)
     "editornotfound": false,
     "encoding": "ascii",
     "encodingerror": null,
     "extensionserror": null, (no-pure !)
     "hgmodulepolicy": "*", (glob)
     "hgmodules": "*mercurial", (glob) (no-pyoxidizer-in-memory !)
     "hgmodules": "*/release/app/hg*", (glob) (pyoxidizer-in-memory !)
     "hgver": "*", (glob)
     "hgverextra": "*", (glob)
     "problems": 0,
     "pythonexe": "*", (glob)
     "pythonimplementation": "*", (glob)
     "pythonlib": "*", (glob)
     "pythonsecurity": [*], (glob)
     "pythonver": "*.*.*", (glob)
     "re2": (true|false), (re)
     "templatedirs": "*mercurial?templates", (glob) (no-pyoxidizer !)
     "templatedirs": "*app?templates", (glob) (pyoxidizer !)
     "username": "test",
     "usernameerror": null,
     "vinotfound": false
    }
   ]
 
 hg debuginstall with no username
   $ HGUSER= hg debuginstall
   checking encoding (ascii)...
   checking Python executable (*) (glob)
   checking Python implementation (*) (glob)
   checking Python version (3.*) (glob)
   checking Python lib (.*[Ll]ib.*)... (re) (no-pyoxidizer !)
   checking Python lib (.*pyoxidizer.*)... (re) (pyoxidizer !)
   checking Python security support (*) (glob)
     TLS 1.2 not supported by Python install; network connections lack modern security (?)
     SNI not supported by Python install; may have connectivity issues with some servers (?)
   checking Rust extensions \((installed|missing)\) (re)
   checking Mercurial version (*) (glob)
   checking Mercurial custom build (*) (glob)
   checking module policy (*) (glob)
   checking installed modules (*mercurial)... (glob) (no-pyoxidizer-in-memory !)
   checking installed modules (*/release/app/hg*)... (glob) (pyoxidizer-in-memory !)
   checking registered compression engines (*zlib*) (glob)
   checking available compression engines (*zlib*) (glob)
   checking available compression engines for wire protocol (*zlib*) (glob)
   checking "re2" regexp engine \((available|missing)\) (re)
   checking templates (*mercurial?templates)... (glob) (no-pyoxidizer !)
   checking templates (*app?templates)... (glob) (pyoxidizer !)
   checking default template (*mercurial?templates?map-cmdline.default) (glob) (no-pyoxidizer !)
   checking default template (*app?templates?map-cmdline.default) (glob) (pyoxidizer !)
   checking commit editor... (*) (glob)
   checking username...
    no username supplied
    (specify a username in your configuration file)
   1 problems detected, please check your install!
   [1]
 
 hg debuginstall with invalid encoding
   $ HGENCODING=invalidenc hg debuginstall | grep encoding
   checking encoding (invalidenc)...
    unknown encoding: invalidenc
 
 exception message in JSON
 
   $ HGENCODING=invalidenc HGUSER= hg debuginstall -Tjson | grep error
     "defaulttemplateerror": null,
     "encodingerror": "unknown encoding: invalidenc",
     "extensionserror": null, (no-pure !)
     "usernameerror": "no username supplied",
 
 path variables are expanded (~ is the same as $TESTTMP)
   $ mkdir tools
   $ touch tools/testeditor.exe
 #if execbit
   $ chmod 755 tools/testeditor.exe
 #endif
   $ HGEDITOR="~/tools/testeditor.exe" hg debuginstall
   checking encoding (ascii)...
   checking Python executable (*) (glob)
   checking Python implementation (*) (glob)
   checking Python version (3.*) (glob)
   checking Python lib (.*[Ll]ib.*)... (re) (no-pyoxidizer !)
   checking Python lib (.*pyoxidizer.*)... (re) (pyoxidizer !)
   checking Python security support (*) (glob)
     TLS 1.2 not supported by Python install; network connections lack modern security (?)
     SNI not supported by Python install; may have connectivity issues with some servers (?)
   checking Rust extensions \((installed|missing)\) (re)
   checking Mercurial version (*) (glob)
   checking Mercurial custom build (*) (glob)
   checking module policy (*) (glob)
   checking installed modules (*mercurial)... (glob) (no-pyoxidizer-in-memory !)
   checking installed modules (*/release/app/hg*)... (glob) (pyoxidizer-in-memory !)
   checking registered compression engines (*zlib*) (glob)
   checking available compression engines (*zlib*) (glob)
   checking available compression engines for wire protocol (*zlib*) (glob)
   checking "re2" regexp engine \((available|missing)\) (re)
   checking templates (*mercurial?templates)... (glob) (no-pyoxidizer !)
   checking templates (*app?templates)... (glob) (pyoxidizer !)
   checking default template (*mercurial?templates?map-cmdline.default) (glob) (no-pyoxidizer !)
   checking default template (*app?templates?map-cmdline.default) (glob) (pyoxidizer !)
   checking commit editor... ($TESTTMP/tools/testeditor.exe)
   checking username (test)
   no problems detected
 
 print out the binary post-shlexsplit in the error message when commit editor is
 not found (this is intentionally using backslashes to mimic a windows usecase).
   $ HGEDITOR="c:\foo\bar\baz.exe -y -z" hg debuginstall
   checking encoding (ascii)...
   checking Python executable (*) (glob)
   checking Python implementation (*) (glob)
   checking Python version (3.*) (glob)
   checking Python lib (.*[Ll]ib.*)... (re) (no-pyoxidizer !)
   checking Python lib (.*pyoxidizer.*)... (re) (pyoxidizer !)
   checking Python security support (*) (glob)
     TLS 1.2 not supported by Python install; network connections lack modern security (?)
     SNI not supported by Python install; may have connectivity issues with some servers (?)
   checking Rust extensions \((installed|missing)\) (re)
   checking Mercurial version (*) (glob)
   checking Mercurial custom build (*) (glob)
   checking module policy (*) (glob)
   checking installed modules (*mercurial)... (glob) (no-pyoxidizer-in-memory !)
   checking installed modules (*/release/app/hg*)... (glob) (pyoxidizer-in-memory !)
   checking registered compression engines (*zlib*) (glob)
   checking available compression engines (*zlib*) (glob)
   checking available compression engines for wire protocol (*zlib*) (glob)
   checking "re2" regexp engine \((available|missing)\) (re)
   checking templates (*mercurial?templates)... (glob) (no-pyoxidizer !)
   checking templates (*app?templates)... (glob) (pyoxidizer !)
   checking default template (*mercurial?templates?map-cmdline.default) (glob) (no-pyoxidizer !)
   checking default template (*app?templates?map-cmdline.default) (glob) (pyoxidizer !)
   checking commit editor... (c:\foo\bar\baz.exe) (windows !)
    Can't find editor 'c:\foo\bar\baz.exe' in PATH (windows !)
   checking commit editor... (c:foobarbaz.exe) (no-windows !)
    Can't find editor 'c:foobarbaz.exe' in PATH (no-windows !)
    (specify a commit editor in your configuration file)
   checking username (test)
   1 problems detected, please check your install!
   [1]
 
 debuginstall extension support
   $ hg debuginstall --config extensions.fsmonitor= --config fsmonitor.watchman_exe=false | grep atchman
   fsmonitor checking for watchman binary... (false)
    watchman binary missing or broken: warning: Watchman unavailable: watchman exited with code 1
 Verify the json works too:
   $ hg debuginstall --config extensions.fsmonitor= --config fsmonitor.watchman_exe=false -Tjson | grep atchman
     "fsmonitor-watchman": "false",
     "fsmonitor-watchman-error": "warning: Watchman unavailable: watchman exited with code 1",
 
 Verify that Mercurial is installable with pip. Note that this MUST be
 the last test in this file, because we do some nasty things to the
 shell environment in order to make the virtualenv work reliably.
 
 On Python 3, we use the venv module, which is part of the standard library.
 But some Linux distros strip out this module's functionality involving pip,
 so we have to look for the ensurepip module, which these distros strip out
 completely.
 On Python 2, we use the 3rd party virtualenv module, if available.
 
   $ cd $TESTTMP
   $ unset PYTHONPATH
 
 #if py3 ensurepip network-io no-pyoxidizer
   $ "$PYTHON" -m venv installenv >> pip.log
 
 Hack: Debian does something a bit different in ensurepip.bootstrap. This makes
 it so that pip thinks the 'wheel' wheel is installed so it can build wheels;
 when it goes to try, however, it shells out to run `python3 -u <setup.py>`,
 that *doesn't* get the 'wheel' wheel, and it fails with an invalid command
 'bdist_wheel'. To fix this, we just delete the wheel from where Debian put it in
 our virtual env. Then pip doesn't think it's installed and doesn't try to build.
   $ rm installenv/share/python-wheels/wheel-*.whl >/dev/null 2>&1 || true
 
 Note: we use this weird path to run pip and hg to avoid platform differences,
 since it's bin on most platforms but Scripts on Windows.
-  $ (syshgenv; ./installenv/*/pip install $TESTDIR/.. >> pip.log)
+  $ (syshgenv; ./installenv/*/pip --no-cache-dir install $TESTDIR/.. >> pip.log)
     Failed building wheel for mercurial (?)
   WARNING: You are using pip version *; however, version * is available. (glob) (?)
   You should consider upgrading via the '$TESTTMP/installenv/bin/python* -m pip install --upgrade pip' command. (glob) (?)
    (?)
   [notice] A new release of pip is available: * -> * (glob) (?)
   [notice] To update, run: * -m pip install --upgrade pip (glob) (?)
   $ ./installenv/*/hg debuginstall || cat pip.log
   checking encoding (ascii)...
   checking Python executable (*) (glob)
   checking Python implementation (*) (glob)
   checking Python version (3.*) (glob)
   checking Python lib (*)... (glob)
   checking Python security support (*) (glob)
   checking Rust extensions \((installed|missing)\) (re)
   checking Mercurial version (*) (glob)
   checking Mercurial custom build (*) (glob)
   checking module policy (*) (glob)
   checking installed modules (*/mercurial)... (glob)
   checking registered compression engines (*) (glob)
   checking available compression engines (*) (glob)
   checking available compression engines for wire protocol (*) (glob)
   checking "re2" regexp engine \((available|missing)\) (re)
   checking templates ($TESTTMP/installenv/*/site-packages/mercurial/templates)... (glob)
   checking default template ($TESTTMP/installenv/*/site-packages/mercurial/templates/map-cmdline.default) (glob)
   checking commit editor... (*) (glob)
   checking username (test)
   no problems detected
 #endif