Update sphinx requirement from <5 to <6

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/5.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v0.1.61611...v5.0.0)

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

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

docs/sphinx-requirements.txt

@@ -1,6 +1,6 @@
 git+https://github.com/gniezen/n3pygments.git
 myst-parser
-sphinx<5
+sphinx<6
 sphinxcontrib-apidoc
 sphinxcontrib-kroki
 sphinx-autodoc-typehints

setup.py

@@ -24,7 +24,7 @@
     "tests": kwargs["tests_require"],
     "docs": [
         "myst-parser",
-        "sphinx < 5",
+        "sphinx < 6",
         "sphinxcontrib-apidoc",
         "sphinxcontrib-kroki",
         "sphinx-autodoc-typehints",