Note: not for backporting to MPL-3.10. Ref: #29766 (comment)

Thanks @timhoffm!

Note for maintainers: it might make sense to merge #29765 (if/when ready) before this one (e.g. increasing overall test coverage briefly before removing stale coverage, rather than removing stale coverage before adding some more).

If you want to replace the other workflows to update 3.10 to 3.11, it would be appreciated.

.github/workflows/cibuildwheel.yml:          python-version: '3.10'
.github/workflows/cibuildwheel.yml:      - name: Build wheels for CPython 3.10
.github/workflows/mypy-stubtest.yml:          python-version: '3.10'
.github/workflows/mypy-stubtest.yml:              sed -e "s!.tox/stubtest/lib/python3.10/site-packages!lib!g" | \
.github/workflows/reviewdog.yml:          python-version: '3.10'
.github/workflows/reviewdog.yml:          python-version: '3.10'
.github/workflows/tests.yml:            python-version: '3.10'
.github/workflows/tests.yml:            # Oldest versions with Py3.10 wheels.
.github/workflows/tests.yml:            python-version: '3.10'
.github/workflows/tests.yml:            python-version: '3.10'
azure-pipelines.yml:              python.version: '3.10'

(And maybe a few more. But I can also do it later.)

@oscargus I could take a look at that, sure - two notes though:

• I think we should keep at least some form of py3.10 continuous integration testing in place until it is no longer supported by matplotlib (e.g. next release, if I understand correctly).
• You are not suggesting to increase the minimum Python version yet, right? I ask based on taking a quick look at Bump minimum Python to 3.10 #28503 and noticing that there are a few other places we'd want to update too, when doing that, I think.

Lets merge this as-is and do a second round of dropping the rest of the 3.10 builds / pushing our minimum up to 3.11.

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout v3.10.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 0d11978c9f933a9fc7a585891b350c09958e034b

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #29796: ci: rotate soon-to-be-unsupported GitHub Actions ubuntu-20.04 runner out of roster'

4. Push to a named branch:

git push YOURFORK v3.10.x:auto-backport-of-pr-29796-on-v3.10.x

5. Create a PR against branch v3.10.x, I would have named this PR:

"Backport PR #29796 on branch v3.10.x (ci: rotate soon-to-be-unsupported GitHub Actions ubuntu-20.04 runner out of roster)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout v3.10.1-doc
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 0d11978c9f933a9fc7a585891b350c09958e034b

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #29796: ci: rotate soon-to-be-unsupported GitHub Actions ubuntu-20.04 runner out of roster'

4. Push to a named branch:

git push YOURFORK v3.10.1-doc:auto-backport-of-pr-29796-on-v3.10.1-doc

5. Create a PR against branch v3.10.1-doc, I would have named this PR:

"Backport PR #29796 on branch v3.10.1-doc (ci: rotate soon-to-be-unsupported GitHub Actions ubuntu-20.04 runner out of roster)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.

@jayaddison (continuing here). Yes, I think that since we now have committed to bump the minimum version to 3.11 for the next release, one may just go all the way. But, yes, there are probably quite a few changes to sort out, not just bumping the work flows.

(I was primarily triggered to request it based on #29840 which was triggered by this PR... Maybe I'll continue in that one.)

@oscargus there's no immediate hurry to push all possible updates through that are enabled by dropping 3.10. Here, we have the immediate need to update the images used in CI, and as part of that it's reasonable to do the 3.11 update on CI.