Fix various pieces of CI bitrot

[cjwatson]

Among other things, this drops support for Python 3.8.

Fixes #427

[cjwatson]

I've done my best here, but I have no idea what's going on with the test failures. Help?

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I've done my best here, but I have no idea what's going on with the test failures. Help?

For starters, try upgrading the werkzeug pin in [dev]?

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Just did so myself and things look a bit better, let me try pushing this.

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Looks like this will need to absorb #426

[cjwatson]

The Python 3.10 test failures in that last run seem about the same as before. I cherry-picked the fix for #426 though, just to try to clear things up slightly.

[cjwatson]

Since GHA likes to stop at the first failure, I tried these locally. py39-twisted_lowest, py39-twisted_latest, py39-twisted_trunk, and py310-twisted_lowest fail. Later versions of Python, and Python 3.10 with later versions of Twisted, succeed.

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Since GHA likes to stop at the first failure, I tried these locally. py39-twisted_lowest, py39-twisted_latest, py39-twisted_trunk, and py310-twisted_lowest fail. Later versions of Python, and Python 3.10 with later versions of Twisted, succeed.

I think the issue is probably that older Twisted no longer works with current Cryptography. I am adding some extra debug logging stuff so that at least i can see what's going on in the httpbin server, and seeing builtins.ValueError: Context has already been used to create a Connection, it cannot be mutated again makes me feel like this is confirmed

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@cjwatson I'm inclined to approve and merge if this turns green; if it were lower priority I'd wait for someone who hadn't worked on it, but we should get trunk back to green ASAP.

[cjwatson]

Thanks for figuring this out!

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Thanks for getting it started!