Build(deps-dev): Update sphinx requirement from <7,>=4 to >=4,<8

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@v4.0.0...v7.2.5)

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

Signed-off-by: dependabot[bot] <[email protected]>

requirements_dev.txt

@@ -34,7 +34,7 @@ pytest
 qutip==4.7.2
 sax==0.8.8  # Pinned for pydantic <v2 compatibility.
 setuptools>=40.8.0
-sphinx>=4,<7
+sphinx>=4,<8
 sphinx-autoapi
 sphinx-autobuild
 sphinx_autodoc_typehints