CI: add CPython 3.12 and PyPy3.10, stop promising untested versions

[pajod]

Resubmitted smaller changeset. Intend to fix the remainder of #3110 later.

• pytest+mac+PyPy3.9 sometimes just hangs, so this one adds an overall timeout to cancel those test runs, deferring the decision of dropping PyPy3.9 early or figuring out why.
• Linting remains broken.. which is okay, this patch does not include any bump in the CPython 3.10 used for CI linting.

Issues:

• Fixes: Suggestion: Drop support for python < 3.7 #3045
• Closes: Version 21.0.1 or higher breaks with python 3.5 #3046

Merge order:

• rebased Document Python 3.7 requirement #3083 and Add Python 3.12 to test matrix and add classifiers #3085 are prepended, and are not needed after merging this one
• suggest merging restore, and from now on CI-test for entry point #3108 before this one
• suggest merging refactor: remove python 2 new-style classes as only python 3.5+ is supported now #2836 after this one

[tilgovi]

I merged #3108. Is this next?

[tilgovi]

Should I merge this now, or is there other stuff you want to land first for conflict / ordering reasons still?

[pajod]

I merged #3108. Is this next?

Yes please, if the CI finishes (or times out in less than the 6 hour default).

EDIT: interesting. now it was just regular slow, and my 10 minute timeout just a little too aggressive for the Github shared resources.
EDIT2: tests failed again, but this time just unrelated trouble with the runners. Will push no-op commit on top if that is required to re-run them.

[benoitc]

note that I am paying for CI, so we should have more resources available. I will re-check