build(deps): bump sphinx from 3.0.4 to 3.4.0

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.0.4 to 3.4.0.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/3.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.0.4...v3.4.0)

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

Author: dependabot-preview[bot]

docs-requirements.txt

@@ -1,4 +1,4 @@
-sphinx==3.0.4
+sphinx==3.4.0
 sphinx-rtd-theme
 sphinx-autodoc-typehints[type_comments]>=1.8.0
 typing-extensions