pythia8 fails to build with Python 3.13.0a1.

include/pybind11/detail/../detail/type_caster_base.h: In function ‘PyThreadState* pybind11::detail::get_thread_state_unchecked()’:
include/pybind11/detail/../detail/type_caster_base.h:565:12: error: ‘_PyThreadState_UncheckedGet’ was not declared in this scope; did you mean ‘PyThreadState_GetUnchecked’?
  565 |     return _PyThreadState_UncheckedGet();
      |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~
      |            PyThreadState_GetUnchecked
According to https://docs.python.org/3.13/whatsnew/3.13.html a new public function has been added:

Add PyThreadState_GetUnchecked() function: similar to PyThreadState_Get(), but don’t kill the process with a fatal error if it is NULL.
The caller is responsible to check if the result is NULL.
Previously, the function was private and known as _PyThreadState_UncheckedGet().
(Contributed by Victor Stinner in gh-108867.)

https://docs.python.org/3.13/whatsnew/3.13.html

For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.13/fedora-rawhide-x86_64/06546830-pythia8/

For all our attempts to build pythia8 with Python 3.13, see:
https://copr.fedorainfracloud.org/coprs/g/python/python3.13/package/pythia8/

Testing and mass rebuild of packages is happening in copr.
You can follow these instructions to test locally in mock if your package builds with Python 3.13:
https://copr.fedorainfracloud.org/coprs/g/python/python3.13/

Let us know here if you have any questions.

Python 3.13 is planned to be included in Fedora 41.
To make that update smoother, we're building Fedora packages with all pre-releases of Python 3.13.
A build failure prevents us from testing all dependent packages (transitive [Build]Requires),
so if this package is required a lot, it's important for us to get it fixed soon.

We'd appreciate help from the people who know this package best,
but if you don't want to work on this now, let us know so we can try to work around it on our side.