update Cython to 3.1.1 by methane · Pull Request #637 · msgpack/msgpack-python
Recent setuptools releases require Python >= 3.9.
https://setuptools.pypa.io/en/latest/history.html#v75-4-0
Maybe it makes sense to delay the SPDX license stuff for a while?
Nitpick: it is Cython 3.1.1, not 3.11 (commit comment, PR title).