MAINT: Deal with pytest 8.0

[larsoner]

See pytest-dev/pytest#10937 (comment), TL;DR is that pytest.warns in 8.0 will re-emit any unmatched warnings. So in effect our options are, for every call where this happens (about 100 according to this run), do one or a combination of:

1. Chain multiple context managers to catch all warnings
2. Add an outer context manager just to swallow other warnings
3. Roll our own warns(...) variant with a reemit=False default

I don't like (3) because the more we specialize our code the more hard it becomes to work with and come from other packages. (2) is the easiest and probably most appropriate for some cases actually where we get multiple warnings -- like in this first test_misc.py we get multiple "event missing" warnings we don't care about and rather than catch a bunch of them, just make sure the one we care about does get emitted. (In the volume source estimate cases this could be dozens of warnings, so impractical there as well.) And (1) could be ideal in some cases.

So I think my plan is to do a combination of (1) and (2) based on judgment of the ~85 currently failing tests. It'll take some time but hopefully end up readable. Okay @drammock ?

Closes #12372

[larsoner]

@drammock we have to do this if we want to do:

with pytest.warns(...), pytest.warns(...):

because on <8 the inner context manager won't reemit the warnings but on >=8 it will.

Alternatively I could change all instances to with _record_warnings(), pytest.warns(...) (i.e., a single pytest.warns being caught) but then we lose the option to have extra specificity.

I don't love either option really... a third option would be to have a with also_warns(...), pytest.warns(...) where also_warns == pytest.warns for 8+ and also_warns == _record_warnings (i.e., noop) when on <8. But this is custom code again, at least for a while until we do want to pin to 8+ then we can substitute pytest.warns for all second_warns. Maybe that's the safest option here?

[larsoner]

Self-merging, now that 8.0 is out we need this