Bump sphinx from 7.3.7 to 8.1.3 in /tests

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 7.3.7 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@v7.3.7...v8.1.3)

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

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

tests/requirements-test.txt

@@ -2,7 +2,7 @@
 pytest==8.3.3
 flake8==7.1.1
 sphinx<7.2 ; python_version < '3.9'
-sphinx==7.3.7; python_version >= '3.9'
+sphinx==8.1.3; python_version >= '3.9'
 mcpl==1.6.2
 yapf==0.40.2
 requests==2.31.0