chore(deps): update sphinx-rtd-theme requirement (#34)

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@1.0.0...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

@@ -18,7 +18,7 @@ classifiers = ["License :: OSI Approved :: Apache Software License"]
 license = { file = "LICENSE" }
 
 [project.optional-dependencies]
-docs = ["toml~=0.10.2", "sphinx>=5,<9", "sphinx-rtd-theme>=1.0,<2.1"]
+docs = ["toml~=0.10.2", "sphinx>=5,<9", "sphinx-rtd-theme>=1.0,<3.1"]
 test = ["pytest>=7.4,<9.0", "pytest-cov>=4,<6"]
 lint = ["pylint>=2.17,<3.4"]