heptapod: add `.gitattributes` file to improve language detection

I am fully aware of the irony.

.gitattributes

@@ -0,0 +1,2 b''
+# So GitLab doesn't think we're using tons of Perl
+*.t -linguist-detectable

tests/test-check-code.t

@@ -1,96 +1,97 b''
 #require test-repo
 
   $ . "$TESTDIR/helpers-testrepo.sh"
   $ check_code="$TESTDIR"/../contrib/check-code.py
   $ cd "$TESTDIR"/..
 
 New errors are not allowed. Warnings are strongly discouraged.
 (The writing "no-che?k-code" is for not skipping this file when checking.)
 
   $ testrepohg locate \
   > -X contrib/python-zstandard \
   > -X hgext/fsmonitor/pywatchman \
   > -X mercurial/thirdparty \
   > -X mercurial/pythoncapi_compat.h \
   > | sed 's-\\-/-g' | "$check_code" --warnings --per-file=0 - || false
   Skipping contrib/automation/hgautomation/__init__.py it has no-che?k-code (glob)
   Skipping contrib/automation/hgautomation/aws.py it has no-che?k-code (glob)
   Skipping contrib/automation/hgautomation/cli.py it has no-che?k-code (glob)
   Skipping contrib/automation/hgautomation/linux.py it has no-che?k-code (glob)
   Skipping contrib/automation/hgautomation/pypi.py it has no-che?k-code (glob)
   Skipping contrib/automation/hgautomation/ssh.py it has no-che?k-code (glob)
   Skipping contrib/automation/hgautomation/try_server.py it has no-che?k-code (glob)
   Skipping contrib/automation/hgautomation/windows.py it has no-che?k-code (glob)
   Skipping contrib/automation/hgautomation/winrm.py it has no-che?k-code (glob)
   Skipping contrib/fuzz/FuzzedDataProvider.h it has no-che?k-code (glob)
   Skipping contrib/fuzz/standalone_fuzz_target_runner.cc it has no-che?k-code (glob)
   Skipping contrib/packaging/hgpackaging/cli.py it has no-che?k-code (glob)
   Skipping contrib/packaging/hgpackaging/downloads.py it has no-che?k-code (glob)
   Skipping contrib/packaging/hgpackaging/inno.py it has no-che?k-code (glob)
   Skipping contrib/packaging/hgpackaging/pyoxidizer.py it has no-che?k-code (glob)
   Skipping contrib/packaging/hgpackaging/util.py it has no-che?k-code (glob)
   Skipping contrib/packaging/hgpackaging/wix.py it has no-che?k-code (glob)
   Skipping hgext/fsmonitor/__init__.py it has no-che?k-code (glob)
   Skipping i18n/polib.py it has no-che?k-code (glob)
   Skipping mercurial/statprof.py it has no-che?k-code (glob)
   Skipping tests/testlib/badserverext.py it has no-che?k-code (glob)
 
 @commands in debugcommands.py should be in alphabetical order.
 
   >>> import re
   >>> commands = []
   >>> with open('mercurial/debugcommands.py', 'rb') as fh:
   ...     for line in fh:
   ...         m = re.match(br"^@command\('([a-z]+)", line)
   ...         if m:
   ...             commands.append(m.group(1))
   >>> scommands = list(sorted(commands))
   >>> for i, command in enumerate(scommands):
   ...     if command != commands[i]:
   ...         print('commands in debugcommands.py not sorted; first differing '
   ...               'command is %s; expected %s' % (commands[i], command))
   ...         break
 
 Prevent adding new files in the root directory accidentally.
 
   $ testrepohg files 'glob:*'
   .arcconfig
   .clang-format
   .editorconfig
+  .gitattributes
   .hgignore
   .hgsigs
   .hgtags
   .jshintrc
   CONTRIBUTING
   CONTRIBUTORS
   COPYING
   Makefile
   README.rst
   hg
   hgeditor
   hgweb.cgi
   pyproject.toml
   rustfmt.toml
   setup.py
 
 Prevent adding modules which could be shadowed by ancient .so/.dylib.
 
   $ testrepohg files \
   > mercurial/base85.py \
   > mercurial/bdiff.py \
   > mercurial/diffhelpers.py \
   > mercurial/mpatch.py \
   > mercurial/osutil.py \
   > mercurial/parsers.py \
   > mercurial/zstd.py
   [1]
 
 Keep python3 tests sorted:
   $ sort < contrib/python3-whitelist > $TESTTMP/py3sorted
   $ cmp contrib/python3-whitelist $TESTTMP/py3sorted || echo 'Please sort passing tests!'
 
 Keep Windows line endings in check
 
   $ testrepohg files 'set:eol(dos)'
   contrib/win32/hg.bat
   contrib/win32/mercurial.ini