chore(deps): Update sphinx-rtd-theme requirement in /docs (#4024)

Updates the requirements on [sphinx-rtd-theme](https://github.com/readthedocs/sphinx_rtd_theme) to permit the latest version.
- [Changelog](https://github.com/readthedocs/sphinx_rtd_theme/blob/master/docs/changelog.rst)
- [Commits](readthedocs/sphinx_rtd_theme@3.0.2...3.1.0)

---
updated-dependencies:
- dependency-name: sphinx-rtd-theme
  dependency-version: 3.1.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

docs/requirements.txt

@@ -1,5 +1,5 @@
 # Defining the exact versions for ReadTheDocs that will make sure things don't break
 sphinx~=8.2.1
-sphinx-rtd-theme~=3.0.2
+sphinx-rtd-theme~=3.1.0
 readthedocs-sphinx-search~=0.3.2
 sphinx-notfound-page~=1.1.0