Update pydocstyle to 2.1.1 and flake8-docstrings to 1.3.0 (#14557)

* Update pydocstyle to 2.1.1 and flake8-docstrings to 1.3.0

* Pydocstyle D401 fixes

tests/helpers/test_entity_platform.py

@@ -336,7 +336,7 @@ def test_raise_error_on_update(hass):
     entity2 = MockEntity(name='test_2')
 
     def _raise():
-        """Helper to raise an exception."""
+        """Raise an exception."""
         raise AssertionError
 
     entity1.update = _raise