Add matrix strategy to test with all supported Python versions

[m-aciek]

No description provided.

[ghost]

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[pradyunsg]

I'll go ahead and merge this, on the basis that this seems like a good idea overall. Holler if you spot something off! :)

[hugovk]

Is it possible to add 3.12/main?

Should the doc-html artifact at https://github.com/python/python-docs-theme/actions/runs/4393087253 also include 3.8-3.10?

Left is main, right is this PR:

[m-aciek]

Is it possible to add 3.12/main?

Yes, definitely, I think it's a good idea, I can add a pull request for that.

Should the doc-html artifact at https://github.com/python/python-docs-theme/actions/runs/4393087253 also include 3.8-3.10?

Actually, we should see the jobs for 3.8-3.10 as failed, as my branch wasn't basing on fresh-fixed master. The missing artifacts were because of failed jobs. It looks like exit code of build_docs.py script is incorrectly zero instead of non-zero for failing build. I will try to confirm that and follow it up in builddocs-script GitHub repository.

That's what the artifacts from the Actions on the theme main branch look like for me (all versions from matrix are there):

[m-aciek]

Please see PR python/docsbuild-scripts#150.

[m-aciek]

I just wanted to share a thought that in case of a need of some changes that would break backwards compatibility we can always decide to pin the theme version in CPython branch and remove a version from matrix. But still it will be easier to spot the breakage and pin the version in advance of releasing such changes having those tests in CI.