[Dependabot]: Update sphinx-rtd-theme requirement

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@2.0.0...3.0.0)

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

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

doc/requirements.txt

@@ -10,7 +10,7 @@ sphinx ~= 7.4
 docutils ~= 0.20
 
 # ReadTheDocs Theme
-sphinx_rtd_theme ~= 2.0.0
+sphinx_rtd_theme ~= 3.0.0
 
 # Sphinx Extenstions
 #sphinxcontrib-actdiag>=0.8.5