Clarify docs on specifying multiple filters with pytest.mark.filterwarnings

[soxofaan]

Specifying multiple filterwarnings filter in the correct order can be a bit confusing.

When using @pytest.mark.filterwarnings as decorator, one has to use the reverse order compared to stdlib's warnings.filterwarnings (because of the order that decorators are evaluated).
When using pytestmark (list of pytest.mark.filterwarnings marks), it's the other way around.

I think this deserves a bit of clarification in the docs

FYI: I'm actually already working on a PR for this

[The-Compiler]

According to the code, it's also possible to pass multiple arguments/filters into one decorator/mark instead of having to have multiple of them:

pytest/src/_pytest/warnings.py

Lines 59 to 61 in 71a35d4

	for mark in item.iter_markers(name="filterwarnings"):
	for arg in mark.args:
	warnings.filterwarnings(*parse_warning_filter(arg, escape=False))

That seems like a much easier and more consistent way to get to the same result, though it looks like the docs don't do a great job at pointing that out either. @soxofaan would you perhaps be interested in opening another PR detailing that a bit more too?

[soxofaan]

Ah that's interesting. I kind of tried something like that by passing a single string with comma-separated filters, following PYTHONWARNINGS, which didn't work.
Passing multiple arguments is indeed cleaner and probably less confusing that the multi-decorator approach.

I'll see if I find some time to do a follow-up PR