CI: Linux py36_locale failures with pytest DeprecationWarning
tests using `async_mark` are failing cc @alimcmaster1 
```
=========================== short test summary info ============================
ERROR pandas/tests/arrays/categorical/test_warnings.py::TestCategoricalWarnings
ERROR pandas/tests/arrays/categorical/test_warnings.py::TestCategoricalWarnings
ERROR pandas/tests/frame/test_api.py::TestDataFrameMisc - pytest.PytestDeprec...
ERROR pandas/tests/frame/test_api.py::TestDataFrameMisc - pytest.PytestDeprec...
ERROR pandas/tests/indexes/test_base.py::TestIndex - pytest.PytestDeprecation...
ERROR pandas/tests/indexes/test_base.py::TestIndex - pytest.PytestDeprecation...
ERROR pandas/tests/resample/test_resampler_grouper.py - pytest.PytestDeprecat...
ERROR pandas/tests/resample/test_resampler_grouper.py - pytest.PytestDeprecat...
ERROR pandas/tests/series/test_api.py::TestSeriesMisc - pytest.PytestDeprecat...
ERROR pandas/tests/series/test_api.py::TestSeriesMisc - pytest.PytestDeprecat...
= 71242 passed, 1936 skipped, 1024 xfailed, 156 warnings, 10 errors in 655.85s (0:10:55) =
```