Bump sphinx from 3.5.1 to 3.5.2 in /requirements/CI

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.5.1 to 3.5.2.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/3.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.5.1...v3.5.2)

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

requirements/CI/requirements.txt

@@ -3,7 +3,7 @@ coverage==5.5
 flake8==3.8.4
 nose==1.3.7
 setuptools-scm==5.0.1
-sphinx==3.5.1
+sphinx==3.5.2
 sphinx-argparse==0.2.5
 sphinx-issues==1.2.0
 sphinx_rtd_theme==0.5.1