Bump sphinx from 3.2.1 to 3.3.1 in /python/requirements/CI-docs

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.2.1 to 3.3.1.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/3.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.2.1...v3.3.1)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

python/requirements/CI-docs/requirements.txt

@@ -5,7 +5,7 @@ h5py==3.1.0
 jsonschema==3.2.0
 numpy==1.19.4
 PyGithub==1.53
-sphinx==3.2.1
+sphinx==3.3.1
 sphinx-argparse==0.2.5
 sphinx-issues==1.2.0
 sphinx_rtd_theme==0.5.0