Bump sphinx-rtd-theme from 1.0.0 to 2.0.0 in /extra_requirements

Bumps [sphinx-rtd-theme](https://github.com/readthedocs/sphinx_rtd_theme) from 1.0.0 to 2.0.0.
- [Changelog](https://github.com/readthedocs/sphinx_rtd_theme/blob/master/docs/changelog.rst)
- [Commits](readthedocs/sphinx_rtd_theme@1.0.0...2.0.0)

---
updated-dependencies:
- dependency-name: sphinx-rtd-theme
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

extra_requirements/requirements-docs.txt

@@ -8,7 +8,7 @@ graphviz==0.20.1
 nbsphinx==0.9.3
 recommonmark==0.7.1
 sphinx==5.2.3
-sphinx_rtd_theme==1.0.0
+sphinx_rtd_theme==2.0.0
 sphinxcontrib_applehelp==1.0.2
 sphinxcontrib_devhelp==1.0.2
 sphinxcontrib_htmlhelp==2.0.0