Bump sphinx from 7.3.7 to 8.1.3 in /client (#747)

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

client/pyproject.toml

@@ -34,7 +34,7 @@ certgrinder = "certgrinder.certgrinder:main"
 [project.optional-dependencies]
 dev = ["twine == 5.1.0", "pre-commit == 4.0.1", "setuptools-scm == 8.1.0", "build==1.2.2.post1"]
 test = ["pytest == 8.2.2", "pytest-cov==5.0.0", "tox == 4.20.0"]
-docs = ["Sphinx==7.3.7", "sphinx-rtd-theme==3.0.2", "sphinx-argparse==0.4.0"]
+docs = ["Sphinx==8.1.3", "sphinx-rtd-theme==3.0.2", "sphinx-argparse==0.4.0"]
 
 [project.urls]
 homepage = "https://github.com/tykling/certgrinder"