chore(deps-dev): bump sphinx from 3.5.3 to 3.5.4

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.5.3 to 3.5.4.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/3.x/CHANGES)
- [Commits](https://github.com/sphinx-doc/sphinx/commits/v3.5.4)

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

dev-requirements.txt

@@ -4,7 +4,7 @@ coveralls==2.2.0
 pytest==6.2.3
 pytest-cov==2.11.1
 attrs~=20.3.0
-Sphinx==3.5.3
+Sphinx==3.5.4
 sphinx-bootstrap-theme==0.7.1
 sphinxcontrib-fulltoc==1.2.0
 sphinxcontrib-websupport==1.2.4