Add support for Python 3.11

[hugovk]

Python 3.11 is set for release in October and now in beta, so it's a good time to start testing.

• https://discuss.python.org/t/the-cursed-release-of-python-3-11-0b4-is-now-available/17274?u=hugovk

Also bump the actions versions in the CI, and https://github.com/actions/setup-python can now take care of caching pip directly, so we can remove the https://github.com/actions/cache config.

[coveralls]

Pull Request Test Coverage Report for Build 2676984916

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 31.118%

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Totals
Change from base Build 1854171453:	0.0%
Covered Lines:	646
Relevant Lines:	2076

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💛 - Coveralls