build(deps-dev): update sphinx requirement

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/v8.0.2/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v4.0.2...v8.0.2)

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

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

setup.cfg

@@ -41,7 +41,7 @@ where = src
 
 [options.extras_require]
 docs =
-    sphinx >=4.0.2, <5.0
+    sphinx >=4.0.2, <9.0
     sphinx-rtd-theme
 #    stanford-theme
 test =