Update sphinx requirement from <8 to <9

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@v0.1.61611...v8.0.2)

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

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

Author: dependabot[bot]

setup.cfg

@@ -45,7 +45,7 @@ dev =
     pytest-xdist<4
     responses==0.25.3
 docs =
-    sphinx<8
+    sphinx<9
     sphinx-issues<5
     furo==2024.5.6