Update sphinx requirement from ==7.2.* to ==7.3.* (#4088)

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.rst)
- [Commits](https://github.com/sphinx-doc/sphinx/compare/v7.2.0...v7.3.5)

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

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

doc/requirements.rtd.txt

@@ -1,4 +1,4 @@
-sphinx==7.2.*
+sphinx==7.3.*
 jinja2==3.1.*
 sphinx-rtd-theme
 sphinxcontrib-httpdomain

doc/requirements.txt

@@ -1,5 +1,5 @@
 -e ../
-sphinx==7.2.*
+sphinx==7.3.*
 jinja2==3.1.*
 sphinx-rtd-theme
 sphinxcontrib-httpdomain