Simplify CI config

[hugovk]

Contributor checklist

• Provided the tests for the changes.
• Assure PR title is short, clear, and good to be included in the user-oriented changelog

Maintainer checklist

• Assure one of these labels is present: backwards incompatible, feature, enhancement, deprecation, bug, dependency, docs or skip-changelog as they determine changelog listing.
• Assign the PR to an existing or new milestone for the target version (following Semantic Versioning).

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Simplifies, replaces and closes #1389.

Saves 70-odd lines of config compare to master and 108 compare to #1389.

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https://github.com/actions/setup-python now has pip caching built in, meaning we can remove a lot of https://github.com/actions/cache config.

• Docs: https://github.com/actions/setup-python#caching-packages-dependencies

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https://github.com/actions/setup-python also now has 3.11-dev so we can remove https://github.com/deadsnakes/action too. One difference here:

• 3.11-dev on https://github.com/actions/setup-python is the latest alpha/beta/RC release
• 3.11-dev on https://github.com/deadsnakes/action is a nightly build

[webknjaz]

One difference here

Yeah, this was one reason to keep it — nightlies are not the same as tagged unstable releases.

[hugovk]

Yup. If testing the 3.11 branch is more important I'll drop that change and keep deadsnakes (687c118), but then 3.11 isn't cached here. 🤔

[hugovk]

Please see #1573 for an alternative.