:func:`pytest.warns` now validates that :func:`warnings.warn` was called with a `str` or a `Warning`.
Currently in Python it is possible to use other types, however this causes an exception when :func:`warnings.filterwarnings` is used to filter those warnings (see `CPython #103577 <https://github.com/python/cpython/issues/103577>`__ for a discussion).
While this can be considered a bug in CPython, we decided to put guards in pytest as the error message produced without this check in place is confusing.