Run tests on Python 3.14

[notatallshaw]

This PR is to run tests for Python 3.14, but not to explicitly support Python 3.14.

I think the earlier we add this the better, as if there's some breaking change in 3.14 that we think shouldn't be breaking it might need to be reported before the CPython beta (i.e. feature freeze).

However, I'm just leaving this as draft for now until I know if there is non-trivial work to do to pass the tests on 3.14.

[notatallshaw]

Seems like most the failures on 3.14 are related to the number of /s that should be at the begining of a path, see previous #13105 and #13062 (comment)

[hroncok]

Seems like most the failures on 3.14 are related to the number of /s that should be at the begining of a path, see previous #13105 and #13062 (comment)

See python/cpython#125974

[hroncok]

pip/src/pip/_internal/utils/urls.py

Line 15 in ffbf6f0

url = urllib.parse.urljoin("file:", urllib.request.pathname2url(path))

[notatallshaw]

Seems more changes (python/cpython#126679) are likely to the output of urljoin before 3.14 beta, I personally don't want to work on fixing these until all changes have landed, and these seem to be the only 3.14 specific failures.

[vstinner]

Would it make sense to skip the failing test on Python 3.14 until Python 3.14 beta 1?

[notatallshaw]

Would it make sense to skip the failing test on Python 3.14 until Python 3.14 beta 1?

If another maintainer wants to do this I would be supportive.

But I’m not volunteering to do so, as it would require a commitment to both turn on and fix those tests in a timely manner, and I can’t guarantee I will remember or have the time when needed. I don't want us to have the illusion that Python 3.14 is green when there are known issues with the test suite.

[ichard26]

Python 3.14 is now in beta so it's worth testing pip again. I'm sure all of the URI tests will need to be updated (again) but otherwise, let's see what else is broken!

[notatallshaw]

@ichard26 FYI I won't have time to work on this for at least a few weeks. Feel free to take over this PR or make a new one if you were interested in fixing 3.14 tests.