maturin: migrate to python@3.10

[Moisan]

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[messense]

The failure is odd, we could try to change

system "python3", "-m", "pip", "install", "hello_world", "--no-index", "--find-links", testpath/"dist"

to

system "python3", "-m", "pip", "install",  testpath/"dist/hello_world*.whl"

[carlocab]

The test probably fails because it's using the CLT-provided python3 in the test block. python@3.10 is keg-only, so won't be in PATH.

[cclauss]

What is the remaining TODO on this PR given that this passes all tests and maturin v0.12.0 supports Python 3.10?

[carlocab]

We don't need to hardcode python@3.10 in multiple places that will need changing eventually.