Update sphinx requirement from ==8.* to ==7.*

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/v7.4.7/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v8.0.0rc1...v7.4.7)

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

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

Author: dependabot[bot]

requirements-readthedocs.txt

@@ -1,6 +1,6 @@
 # keep synchronous to src/VERSION.inc
 pytidyhtml5 == 2024.10.24
 
-sphinx == 8.*
+sphinx == 7.*
 sphinx_autodoc_typehints == 2.*
 sphinx_rtd_theme == 3.*