⬆️ Update sphinx-rtd-theme requirement from ~=2.0 to >=2,<4

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...3.0.1)

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

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

pyproject.toml

@@ -53,7 +53,7 @@ testing-no-myst = [
 
 theme-furo = ["furo~=2024.7.18"]
 theme-pydata = ["pydata-sphinx-theme~=0.15.2"]
-theme-rtd = ["sphinx-rtd-theme~=2.0"]
+theme-rtd = ["sphinx-rtd-theme>=2,<4"]
 theme-sbt = ["sphinx-book-theme~=1.1"]
 theme-im = ["sphinx-immaterial~=0.12.2"]