Bump sphinx from 4.0.2 to 4.2.0

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 4.0.2 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@v4.0.2...v4.2.0)

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

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

setup.py

@@ -36,7 +36,7 @@
 extras_require = {
     'voice': ['PyNaCl>=1.3.0,<1.5'],
     'docs': [
-        'sphinx==4.0.2',
+        'sphinx==4.2.0',
         'sphinxcontrib_trio==1.1.2',
         'sphinxcontrib-websupport',
     ],