gh-111758: Run UBSan in GitHub Actions

[encukou]

This adds a --with-undefined-behavior-sanitizer CI run, modeled after the TSan one.

The runtime should be less than 13 minutes, well below Windows runs.

• Issue: CI should run Undefined Behavior Sanitizer (UBSAN), as already done for ASAN #111758

[hugovk]

There's a lot of duplicate boilerplate in reusable-tsan.yml and reusable-ubsan.yml, we can combine them into a single reusable workflow, and reduce future maintenance.

Something like this: hugovk@39f6c91

Note this is from this morning, and doesn't include your three recent commits.

I'm also happy to do this in a followup if you prefer.

[encukou]

I'm also happy to do this in a followup if you prefer.

Yes, I think it's better as a follow-up. Maybe in a week or so, to let the job settle down? It's easier to edit an independent copy :)
Thank you for starting on it though!

[hugovk]

I think the configure failure:

https://github.com/python/cpython/actions/runs/15706865183/job/44254688889?pr=135578

is because this key is identical to the one in reusable-tsan.yml, so let's add ubsan or something in here:

Suggested change

	key: ${{ github.job }}-${{ env.IMAGE_OS_VERSION }}-${{ inputs.config_hash }}
	key: ${{ github.job }}-ubsan-${{ env.IMAGE_OS_VERSION }}-${{ inputs.config_hash }}

[encukou]

ubsan is part of github.job. It's using a cache from before I added the latest commits.
I removed that cache and will restart the job. (GitHub will allow that after all the other ones finish).