Check GIL, rather than Python version

[radarhere]

Suggestion for python-pillow#8200

At the moment, 3.13-dev installs 3.13.0b2+, and 3.13 installs 3.13.0b2.

In a few months, 3.13-dev will become the same as 3.13. So it seems to me we can just remove the '-dev' suffix now and get it over with.

[hugovk]

Hmm, I think for the time being it might be better to test a nightly build rather than the last tagged one, because things are still being fixed quite regularly upstream for free-threaded and it will be good to help catch things earlier.

There's also some issue with deadsnakes right now, 3.13 is b2 from 8th June instead of b3 from 27th June, 3.13-dev is from 27th June instead of a recent nightly.

I've reported these:

• deadsnakes/action: 3.13 is 3.13.0b2 not 3.13.0b3 deadsnakes/issues#289
• deadsnakes/action: 3.13-dev nightly is 3.13.0b2+ not 3.13.0b3+ deadsnakes/issues#290

[radarhere]

Ok, I've removed that switch. What about the part that is left - checking GIL variables, rather than the Python version?

[hugovk]

Thanks, this is better, as we may switch to actions/setup-python when they add support, and add 3.14+ later.

[radarhere]

Hmm, I think for the time being it might be better to test a nightly build rather than the last tagged one, because things are still being fixed quite regularly upstream for free-threaded and it will be good to help catch things earlier.

We're now at rc2, so I expect things to be pretty stable at this point. Is it time to switch to 3.13?

[hugovk]

Things should be very stable, and there won't be many non-docs changes made to the 3.13 branch before 3.13.0.

But if something does get in, which subsequently breaks things for us, it will be much better to catch it before the big 3.13.0, and get it fixed before then.