ci: Add 3.15 in CI

[clin1234]

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[davidhewitt]

I added full build, if you want to fixup merge conflict we can see what initial results are.

[bschoenmaeckers]

You should bump cpython’s max-version in pyo3-ffi/cargo.toml to 1.15.

[Tpt]

You should bump cpython’s max-version in pyo3-ffi/cargo.toml to 1.15.

cpython 3.15 C-API is I think still moving, wouldn't it better to keep the error message and use UNSAFE_PYO3_SKIP_VERSION_CHECK until the API is stabilized? I am a bit afraid we ship a PyO3 version that end up broken on cpython 3.15 released versions

[davidhewitt]

You should bump cpython’s max-version in pyo3-ffi/cargo.toml to 1.15.

cpython 3.15 C-API is I think still moving, wouldn't it better to keep the error message and use UNSAFE_PYO3_SKIP_VERSION_CHECK until the API is stabilized? I am a bit afraid we ship a PyO3 version that end up broken on cpython 3.15 released versions

Agreed, we should not declare support for 3.15 properly until 3.15 is in beta.

In #5093 (comment) I wrote some thoughts about maybe how we could support 3.15 for development.