Bump tox from 4.15.1 to 4.16.0 in /client

Bumps [tox](https://github.com/tox-dev/tox) from 4.15.1 to 4.16.0.
- [Release notes](https://github.com/tox-dev/tox/releases)
- [Changelog](https://github.com/tox-dev/tox/blob/main/docs/changelog.rst)
- [Commits](tox-dev/tox@4.15.1...4.16.0)

---
updated-dependencies:
- dependency-name: tox
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

client/pyproject.toml

@@ -33,7 +33,7 @@ certgrinder = "certgrinder.certgrinder:main"
 
 [project.optional-dependencies]
 dev = ["twine == 5.1.0", "pre-commit == 3.7.1", "setuptools-scm == 8.1.0", "build==1.2.1"]
-test = ["pytest == 8.2.2", "pytest-cov==5.0.0", "tox == 4.15.1"]
+test = ["pytest == 8.2.2", "pytest-cov==5.0.0", "tox == 4.16.0"]
 docs = ["Sphinx==7.3.7", "sphinx-rtd-theme==2.0.0", "sphinx-argparse==0.4.0"]
 
 [project.urls]