Use Python 3.8 & 3.12 in CI builds

[scy]

Oldest and most recent supported versions.

[scy]

uvloop currently does not support 3.12 yet: MagicStack/uvloop#567

I’ve subscribed to that issue and will update this PR once there’s been a release.

[scy]

Okay, now the issue is that httptools doesn’t have a wheel available for Python 3.12, and building it from source fails.

I guess we’ll wait for MagicStack/httptools#94 to be resolved.

We’re pulling httptools as part of uvicorn[standard]. Uvicorn would run without it, but I’d rather not specify its [standard] dependencies (sans httptools) by hand.

[scy]

Okay, now we’re blocked by flake8-quotes. Python 3.12 allows expressions in f-strings to use the same quotes as the f-string itself, e.g.

x = f"{foo["bar"]}"

However, Python < 3.12 doesn’t. Now, flake8-quotes complains that we’re using single quotes inside of our f-strings, but we have to to maintain backwards compatibility.

I won’t disable that check (Q000) because it applies both to quotes outside and inside of f-strings, so we’ll lose most of our quote checking. On the other hand, flake8-quotes seems not exactly well maintained. There’s no maintainer activity in the respective issue.

Maybe we’ll just have to move to black.

[scy]

Since flake8-quotes still isn't ready for 3.12 due to lacking a maintainer, I've removed flake8 completely and instead went for Ruff, which is better in the long run anyway.

Ruff is obviously throwing lots of errors for our existing codebase now, which is why I've set it to only report errors, but not cause the build (or test.sh) to fail. I'll address these errors (either fixing them, or adding ignore rules) in a follow-up PR.