Fix Windows compiler-finding logic to work with setuptools 74

[neworderofjamie]

pypa/setuptools#4600 removes the setuptools.msvc module which we use for finding the Visual Studio compiler in genn_model.py. In #636 I have pinned the setuptools version but we need to fix properly. This is affecting lots of projects so hopefully will be able to borrow someone else's solution e.g. cupy/cupy#8568.