Add further support for PyPy3.12 v8.0.0

[vstinner]

PyUnstable_Object_IsUniquelyReferenced(), PyUnstable_TryIncRef() and PyUnstable_EnableTryIncRef() are no longer available on PyPy.

[vstinner]

Great! The pypy3.12 job ran successfully with this Python version:

Python 3.12.14 (e778e9989a67, Sep 18 2026, 11:18:35)
[PyPy 8.0.0 with GCC 14.2.1 20250110 (Red Hat 14.2.1-11)]

[vstinner]

Ah, when I merged the PR, the author Hugo became the co-author, and me the co-author became the author. That's surprising.

[vstinner]

Thanks @hugovk for your contribution! It's great to support PyPy 3.12 early. I was surprised, pypy3.12 is already available on GitHub Actions.

[hugovk]

And thanks for updating this! PyPy3.12 now passes Pillow's tests: python-pillow/Pillow#10047.

Yeah, GitHub Actions has automation in place so setup-python will pick up CPython and PyPy updates really quickly. They check https://downloads.python.org/pypy/versions.json for PyPy.

Initially, it'll install the newer Python on-demand in the runner image, which is a little slower, but not usually noticeable. It'll then get cached into the image a bit later.