More robust check of bash version

[koliyo]

More robust check of bash version.

Specifically on windows with git-bash, where python is the normal windows python install

Also use --norc flag to avoid recursively loading .bashrc (which can happen when the click completion loading does not work properly)

Testing should not require any additional tests, but rather make sure to run the existing shell completion tests on multiple platforms, eg Linux, Mac, Windows. Or how do you otherwise recommend adding tests for this?

• fixes Shell completion bash version check fail in git-bash on windows #2638

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.

[koliyo]

Would appreciate some feedback if this is not considered completed. As mentioned, automated testing of this is very context specific, so not sure how, or if, this should be added.

Regarding tox test, tox actually fails locally on my mac, but in a completely unrelated section. NOTE: this also fails in main!

typing: commands[0]> mypy
src/click/utils.py:492: error: Statement is unreachable  [unreachable]
        return os.path.join(
        ^
src/click/_termui_impl.py:616: error: Statement is unreachable  [unreachable]
        try:
        ^
Found 2 errors in 2 files (checked 16 source files)
typing: exit 1 (19.01 seconds) /Users/nils/Work/misc/click> mypy pid=19222
typing: FAIL ✖ in 24.66 seconds

My branch has the same test result as main.