test-install: glob instance of "python" in warning

If run with something else (e.g. python3.12) the message says "python3.12" so we
just glob that away.

tests/test-install.t

@@ -220,7 +220,7 since it's bin on most platforms but Scr
   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: python -m pip install --upgrade pip (?)
+  [notice] To update, run: * -m pip install --upgrade pip (glob) (?)
   $ ./installenv/*/hg debuginstall || cat pip.log
   checking encoding (ascii)...
   checking Python executable (*) (glob)