Update sphinx requirement from ~=5.2.3 to ~=5.3.0 (#123)

Updates the requirements on [sphinx](https://github.com/sphinx-doc/sphinx) to permit the latest version.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES)
- [Commits](sphinx-doc/sphinx@v5.2.3...v5.3.0)

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

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Author: dependabot[bot]

requirements-docs.txt

@@ -11,6 +11,6 @@
 # setup.py.
 ipython ~=7.34.0
 numpydoc ~=1.5
-sphinx ~=5.2.3
+sphinx ~=5.3.0
 sphinx-copybutton ~=0.5.0
 sphinx_rtd_theme ~=1.0.0