Allows for filtering of PytestCacheWarning.
Using `_issue_warning_captured` is not necessary here, and was probably
only used because the cacheprovider misses warnings during
`pytest_sessionfinish`, which is also fixed here.
I think the usage of `_issue_warning_captured` can be removed/reduced
further, but also that this is good enough for now.
Ref: https://github.com/pytest-dev/pytest/issues/6681.