Bump sphinx from 3.5.4 to 4.0.1

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.5.4 to 4.0.1.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/4.x/CHANGES)
- [Commits](https://github.com/sphinx-doc/sphinx/compare/v3.5.4...v4.0.1)

Signed-off-by: dependabot[bot] <support@github.com>

requirements-dev.txt

@@ -9,7 +9,7 @@ selenium==3.141.0
 twine==3.4.1
 Pallets-Sphinx-Themes==2.0.0
 docutils==0.16
-Sphinx==3.5.4
+Sphinx==4.0.1
 sphinx-issues==1.2.0
 sphinx-jinja==1.1.1
 sphinx-tabs==3.0.0