MAINT: Updates for pytest 8.1 and python 3.12

[larsoner]

Supersedes #65

Modernizes some stuff:

• Updates for Pytest 8.1
• Use packaging to get module versions rather than distutils (which is gone in 3.12)
• Set Python min to 3.8 (3.7 is EOL)
• Set pytest min to 6 (almost 4 years old)
• Remove six because with 3.8 min we can
• Test on CI and adapt to 3.12

If it's not desired to drop python_version < 3.8 I can get rid of all that stuff and restore tests etc. This just seemed like the cleanest / most maintainable way forward to me!

[larsoner]

... and pytest 6 came out June 2020, so almost 4 years ago. I think it's okay to require that as a minimum as well. (Anyone on an ancient version of pytest can stick with an older version of pytest-harvest, no?)

[larsoner]

This is now hitting smarie/python-pytest-cases#330 I think (found from pytest-dev/pytest#11868 (comment)) but otherwise is in good shape I think! So for now I'll get rid of the -latest case.

[smarie]

Great stuff @larsoner ! Thanks so much for spending time to work on this.

I'll switch the backend to vitualenv first, so I'll start from this PR #70

Then I'll merge interesting stuff from your branch in.
Hopefully this will happen in the upcoming days, I'll keep you posted

[smarie]

I merged the PR to release a first version 1.10.5 with some of your fixes and others.

I am now totally in favour of moving forward with your proposals (python 3.8 and pytest 6). Could you just update this PR to the latest, I'll have a look afterwards. No particular hurry of course.

[larsoner]

@smarie looks like the conflicts are bad, feel free to take over in a new PR if you want!