chore(deps): update sphinx requirement from <5,>=4.0.0 to >=4.0.0,<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/master/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v4.0.0...v8.1.0)

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

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

Author: dependabot[bot]

pyproject.toml

@@ -46,7 +46,7 @@ dependencies = [
 [project.optional-dependencies]
 docs = [
     "enum-tools",
-    "sphinx>=4.0.0,<5",
+    "sphinx>=4.0.0,<9",
     "sphinx-autobuild",
     "sphinx-toolbox",
     "sphinxcontrib_trio",