CI running on obsolete Python 3.7

[LourensVeen]

Describe the bug
The Python 3.10 CI run fails with ModuleNotFoundError: No module named 'distutils.msvccompiler'. I'm not sure why it's trying to find an MSVC Fortran compiler on Linux, but there we are. Looks like downgrading setuptools to <65 may help.

[LourensVeen]

Ah, turns out that that is an old run, and #1071 turned it off. That doesn't fix the problem though, and Python 3.7 is no longer supported so we do need to upgrade the CI to newer Pythons. I'll have to adapt the CI to the new build system anyway, so we'll pick that up then. Let's keep this, with a different title, to make sure I don't forget.