Update sphinx requirement from ~=5.3.0 to ~=6.1.3

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@v5.3.0...v6.1.3)

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

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docs/requirements-doc.txt

@@ -1,5 +1,5 @@
 -e .
 myst-parser~=0.19
-sphinx~=5.3.0
+sphinx~=6.1.3
 furo==2022.12.7
 types-docutils~=0.19