build(deps): update sphinx requirement from <8.0.0 to <9.0.0

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/v8.1.3/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v0.1.61611...v8.1.3)

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

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

pyproject.toml

@@ -60,7 +60,7 @@ lint = [
     "ruff",
 ]
 docs = [
-    "sphinx<8.0.0",
+    "sphinx<9.0.0",
     "sphinx-rtd-theme",
     "sphinxcontrib-napoleon",
     "nbsphinx",