Add Python 3.9 and 3.10 to the testing

[cclauss]

https://pythoninsider.blogspot.com/2021/10/python-3100-is-available.html

"3.10" must be quoted in YAML. https://dev.to/hugovk/the-python-3-1-problem-85g

[nicoddemus]

Thanks @cclauss!

I fixed a few things, but there's also a bunch of Python version checks that needs updating:

https://github.com/cclauss/nose2pytest/blob/df42b8acc427e18d837fdc3685fb41a350adad3c/nose2pytest/script.py#L93-L112

[cclauss]

Yes. I looked briefly at them and https://github.com/python/cpython/tree/main/Lib/lib2to3 and could not make sense of how they are derived.

Hopefully, time for a new release of nose2pytest given that nose.tools.assert_equals() will raise an AttributeError on Python >= 3.10 and the PyPI version of nose2pytest is far less powerful than the current code in this repo.

[nicoddemus]

Yes, see #15