Update sphinx requirement from <8 to <9 (#484)

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:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

pyproject.toml

@@ -42,7 +42,7 @@ dev = [
     "responses==0.25.3",
 ]
 docs = [
-    "sphinx<8",
+    "sphinx<9",
     "sphinx-issues<5",
     "furo==2024.7.18",
 ]