Sphinx 4.3.0 will be needed for Python 3.10

Author: hugovk

doc/requirements.txt

@@ -1,3 +1,6 @@
-sphinx==4.1.2
+# TODO Temporary until Sphinx 4.3.0 released with Python 3.10 support:
+# https://github.com/sphinx-doc/sphinx/pull/9712
+sphinx==4.1.2;python_version<="3.9"
+git+git://github.com/sphinx-doc/sphinx@f13ad80#egg=sphinx;python_version>="3.10"
 sphinx_rtd_theme
 sphinx-autodoc-typehints