Update sphinx-rtd-theme requirement from ~1.2 to ~1.3 (#65)

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@1.2.0...1.3.0)

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

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

Author: dependabot[bot]

pyproject.toml

@@ -35,7 +35,7 @@ pytest-cov = "~4.1"
 pytest-unordered = "~0.5"
 pre-commit = "~3.3"
 Sphinx = "~6.2"
-sphinx-rtd-theme = "~1.2"
+sphinx-rtd-theme = "~1.3"
 sphinxcontrib-napoleon = "~0.7"
 m2r = "~0.3"
 third-party-license-file-generator = "~2023.2"