Bump tox from 4.20.0 to 4.21.2

Bumps [tox](https://github.com/tox-dev/tox) from 4.20.0 to 4.21.2.
- [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@4.20.0...4.21.2)

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

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

pyproject.toml

@@ -53,7 +53,7 @@ dev = [
     "pre-commit == 3.8.0 ; python_version >= '3.9'",
     "pytest == 8.3.3",
     "setuptools_scm == 8.1.0",
-    "tox == 4.20.0",
+    "tox == 4.21.2",
 ]
 # Docs are always built on a specific Python version; see RTD and tox config files,
 # and the docs contribution guide.