Infra: Test Python 3.11 beta

[hugovk]

Due to the recent delays in the 3.11 beta, it's very important to test it as widely as possible to help find issues before RC1.

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

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Because we have test warnings turned into errors, temporarily ignore these in dependencies:

• Awaiting release of Move away from cgi.parse_header python-babel/babel#873 in Babel 2.11, due 2022-08-01 https://github.com/python-babel/babel/milestone/6?closed=1
• Awaiting imghdr is deprecated and slated for removal in Python 3.13 sphinx-doc/sphinx#10440

Also skip testing 3.11 on Windows because lxml isn't yet available.

[CAM-Gerlach]

Great that we're doing this; thanks @hugovk . A couple comments, one small and one not so small...

[CAM-Gerlach]

Alternatively, it might be better to just use the matrix for the test workflow, since its purpose is the test any build system changes, whereas the render job runs on every PR and push that's mostly just PEP content updates, so it would substantially increase CI load (and the probability of random failures) for relatively little gain there, no?

[hugovk]

Where projects may often test with pre-release Pythons, they rarely build docs, so building docs is a good way to increase coverage of neglected code paths.

That's how I found a release blocker for 3.11 (and a non-blocker too) :)

[CAM-Gerlach]

Sure, I'm just suggesting only running the dev Python matrix job to build the PEPs with Sphinx when the test workflow is triggered, i.e. when some sort of infra-related change is made, rather than on every PR and push. The frequency of PEP infra changes is still typically substantially higher than that of CPython beta releases, and that avoids 1-2 orders of magnitude of extra CI bandwidth, and the main author-facing CIs suddenly starting to fail inexplicably (to authors) on PRs and main when a new CPython beta version is released, as opposed to on PEP editor/infra contributor PRs where it can be recognized and dealt with properly.

[hugovk]

Infra: update JamesIves/github-pages-deploy-action

(Edit: oops, this was meant to be the batch commit comment, the two buttons are right next to each other!)

[CAM-Gerlach]

Sorry, thought I'd approved this! LGTM, thanks @hugovk

FYI, we could also just use @v4 now with the GitHub pages action like we do with the others, if we didn't want to have to be bumping the version manually all the time.

[hugovk]

Good idea, done!