Update pytest warning filter for older Sphinx versions

Author: domdfcoding

tox.ini

@@ -381,6 +381,7 @@ filterwarnings =
     always:'cgi' is deprecated and slated for removal in Python 3.13:DeprecationWarning
     always:The hookimpl pytest_configure uses old-style configuration options:pytest.PytestDeprecationWarning
     always:mypy_extensions.TypedDict is deprecated, and will be removed in a future version. Use typing.TypedDict or typing_extensions.TypedDict instead.:DeprecationWarning
+    always:The `docutils.parsers.rst.directive.html` module will be removed in Docutils 2.0. Since Docutils 0.18, the "Meta" node is defined in `docutils.parsers.rst.directives.misc`:DeprecationWarning
 markers = sphinx