Bump sphinx from 7.4.7 to 8.1.3

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 7.4.7 to 8.1.3.
- [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@v7.4.7...v8.1.3)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-version: 8.1.3
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

poetry.lock

@@ -100,7 +100,7 @@ deptry = ">=0.16.2,<0.25.0"
 tbump = "^6.11.0"
 
 [tool.poetry.group.docs.dependencies]
-sphinx = ">=5.3,<8.0"
+sphinx = ">=5.3,<9.0"
 sphinx-immaterial = ">=0.11,<0.13"
 
 [tool.pytest.ini_options]