Bump sphinx-rtd-theme from 0.5.1 to 0.5.2

Bumps [sphinx-rtd-theme](https://github.com/readthedocs/sphinx_rtd_theme) from 0.5.1 to 0.5.2.
- [Release notes](https://github.com/readthedocs/sphinx_rtd_theme/releases)
- [Changelog](https://github.com/readthedocs/sphinx_rtd_theme/blob/master/docs/changelog.rst)
- [Commits](https://github.com/readthedocs/sphinx_rtd_theme/compare/0.5.1...0.5.2)

Signed-off-by: dependabot[bot] <[email protected]>
(cherry picked from commit 9940fc39b33c117f93e9c43657efeb1b75d3ccbe)

requirements.txt

@@ -4,7 +4,7 @@
 # https://github.com/readthedocs/readthedocs.org/blob/master/requirements/pip.txt
 # https://github.com/readthedocs/readthedocs.org/blob/master/requirements/local-docs-build.txt
 sphinx==3.5.2
-sphinx_rtd_theme==0.5.1
+sphinx_rtd_theme==0.5.2
 
 # Code tabs extension for GDScript/C#
 # Stay on 1.3.0 until https://github.com/readthedocs/readthedocs-sphinx-search/issues/82 is fixed.