Work around Sphinx issue with Python 3.10 and UnionType

Author: domdfcoding

tests/conftest.py

@@ -1,10 +1,16 @@
 # stdlib
 import pathlib
+import sys
 
 # 3rd party
 import pytest
 from sphinx.testing.path import path
 
+if sys.version_info >= (3, 10):
+	# stdlib
+	import types
+	types.Union = types.UnionType
+
 pytest_plugins = ("sphinx.testing.fixtures", "coincidence")