CI: add llvm/clang sanitizer tests

[ngoldbaum]

Closes #25875.

Should fix the test hang in #26307.

[charris]

Seems to be hung.

[ngoldbaum]

Darn it's hanging in the same place as the gcc_sanitizers test used to hang.

I added faulthander_timeout which should prevent hangs and hopefully let us get a traceback if this happens again. I'll add it to the main branch as well. I'll also increase the timeout if 120 seconds is too short.

[ngoldbaum]

I've manually run the tests several times but haven't been able to reproduce the hang. Let me know if you notice this job hanging after merging this PR. I'll try to keep an eye on the action run log.

[charris]

The documentation backport hung, #26312. Let's see how this goes.

[charris]

Thanks Nathan.

[rgommers]

You probably want to close this backport PR I think. There's little need for having sanitizers in the maintenance branch, and if there's still potential reliability problems then it's best to continue improving things in main.

[ngoldbaum]

We turned on the workflow again, but the backport branch still had the old definition. This was supposed to ensure there wouldn't be test hangs on the backport branch.

[charris]

We will still need to disable the test in the 2.0.x branch.