MAINT: Replace Python3.8 by Python3.9.

[charris]

We will drop Python3.8 in NumPy 1.25. This PR updates the ci tests and wheel builds to use 3.9.

A few observations in getting this working:

• PyPy 3.9 isn't ready, it fails some tests, it is left at 3.8.
• The latest cibuildwheel@v2.11.4 fails on 32 bit Windows, cibuildwheel@2.11.2 works.

The failing PyPy 3.9 tests aren't terrible, we could skip them, but I would rather not at this point.

After this goes in, I'll make another PR using cibuildwheel@v2.11.4 to generate errors so I can report them upstream. We will need this fixed so that later versions with Python 3.12 will work when we begin to support it.

[charris]

I didn't touch Cygwin in this first trial. Let's what problems the other test have.

[charris]

@seiko2plus Is the EXPECT_CPU_FEATURES environment variable still needed for the aarch64 builds? I moved it from the Python 3.8 build to the Python 3.9 build.

[seiko2plus]

Is the EXPECT_CPU_FEATURES environment variable still needed for the aarch64 builds?

Just one build is needed to test the sanity of the infrastructure in case of any sudden changes lead to breaking the compile-time detection of CPU features.

[seberg]

LGTM, not merging for a bit in case anyone else had thoughts here.

[charris]

Note that python 3.10 and 3.11 are also available. I chose 3.9 as most likely to be compatible with our other documentation dependencies.

[seberg]

OK, lets just get it in, we can always follow up, thanks Chuck.

[charris]

@mattip Are you still working to get PyPy 3.9 up for NumPy?

[mattip]

I am waiting for cibuildwheel to release a version that supports pypy + macos + arm64, which is progessing in pypa/cibuildwheel#1372