deps: bump tox from 3.27.1 to 4.21.1

Bumps [tox](https://github.com/tox-dev/tox) from 3.27.1 to 4.21.1.
- [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@3.27.1...4.21.1)

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

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

requirements_test.txt

@@ -1,6 +1,6 @@
 # Used for testing
 mypy
 check-python-versions
-tox==3.27.1
+tox==4.21.1
 tox-current-env
 pytest