Remove xfails related to SerializeableLock (#8591)

Author: kmuehlbauer

xarray/tests/test_backends.py

@@ -442,8 +442,6 @@ def test_pickle(self) -> None:
 
     @pytest.mark.filterwarnings("ignore:deallocating CachingFileManager")
     def test_pickle_dataarray(self) -> None:
-        if not has_dask:
-            pytest.xfail("pickling requires dask for SerializableLock")
         expected = Dataset({"foo": ("x", [42])})
         with self.roundtrip(expected, allow_cleanup_failure=ON_WINDOWS) as roundtripped:
             with roundtripped: