chore(deps-dev): bump sphinx from 3.5.4 to 4.2.0

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.5.4 to 4.2.0.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/4.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.5.4...v4.2.0)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

dev-requirements.txt

@@ -3,7 +3,7 @@ coveralls==3.2.0
 pytest==6.2.5
 pytest-cov==2.12.1
 twine==3.4.2
-sphinx==3.5.4
+sphinx==4.2.0
 sphinx-bootstrap-theme==0.7.1
 sphinxcontrib-fulltoc==1.2.0
 sphinxcontrib-websupport==1.2.4