borgbackup fails to build with Python 3.10.0a5.

src/borg/algorithms/msgpack/_unpacker.cpp:2332:17: error: ‘PyObject_AsReadBuffer’ was not declared in this scope; did you mean ‘PyObject_GetBuffer’?
 2332 |     __pyx_t_2 = PyObject_AsReadBuffer(__pyx_v_obj, ((void const **)__pyx_v_buf), __pyx_v_buffer_len); if (unlikely(__pyx_t_2 == ((int)-1))) __PYX_ERR(0, 152, __pyx_L1_error)
      |                 ^~~~~~~~~~~~~~~~~~~~~
      |                 PyObject_GetBuffer
error: command '/usr/bin/gcc' failed with exit code 1

https://docs.python.org/3.10/whatsnew/changelog.html#id16

bpo-41103: PyObject_AsCharBuffer(), PyObject_AsReadBuffer(), PyObject_CheckReadBuffer(), and PyObject_AsWriteBuffer() are removed. Please migrate to new buffer protocol; PyObject_GetBuffer() and PyBuffer_Release().

For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.10/fedora-rawhide-x86_64/01951890-borgbackup/

For all our attempts to build borgbackup with Python 3.10, see:
https://copr.fedorainfracloud.org/coprs/g/python/python3.10/package/borgbackup/

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 3.10:
https://copr.fedorainfracloud.org/coprs/g/python/python3.10/

Let us know here if you have any questions.

Python 3.10 will be included in Fedora 35. To make that update smoother, we're building Fedora packages with early pre-releases of Python 3.10.
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.