Update sphinx-rtd-theme requirement from >=3.0 to >=3.1.0 (#584)

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@3.0.0...3.1.0)

---
updated-dependencies:
- dependency-name: sphinx-rtd-theme
  dependency-version: 3.1.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

docs/requirements.txt

@@ -2,4 +2,4 @@
 sphinx
 sphinx-autoapi
 sphinx-copybutton
-sphinx-rtd-theme>=3.0
+sphinx-rtd-theme>=3.1.0

pyproject.toml

@@ -48,7 +48,7 @@ dev = [
     "sphinx",
     "sphinx-autoapi",
     "sphinx-copybutton",
-    "sphinx-rtd-theme>=3.0",
+    "sphinx-rtd-theme>=3.1.0",
 ]
 
 [build-system]