[DEV] Update sphinx-rtd-theme requirement from ~=2.0 to >=2,<4 (#1089)

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

pyproject.toml

@@ -53,7 +53,7 @@ lint = [
 ]
 docs = [
     "sphinx>=7,<9",
-    "sphinx-rtd-theme~=2.0",
+    "sphinx-rtd-theme>=2,<4",
     "sphinx-book-theme~=1.0",
     "sphinx-copybutton~=0.5",
     "sphinx_design~=0.6",