TST: filter warnings for is_extension_type deprecation
Follow up on https://github.com/pandas-dev/pandas/pull/29457
cc @jbrockmendel  I'm surprised we dont have better tests for is_extension_array_dtype.  LGTM. > What's this referring to?

the need for `test_is_extension_array_dtype` this implements I assume it's verifying that `is_extension_array_dtype` is indeed a drop-in replacement for all the (tested) cases of `is_extension_dtype`. Some are probably duplicative. > I assume it's verifying that is_extension_array_dtype is indeed a drop-in replacement for all the (tested) cases of is_extension_dtype.

Yes, but Brock's comment was about that this was needed, because `is_extension_array_dtype` did not yet have its own dedicated tests in `test_common.py` (it has some indirect tests in the extension array tests)