build(deps-dev): bump platformdirs from 4.1.0 to 4.2.1

Bumps [platformdirs](https://github.com/platformdirs/platformdirs) from 4.1.0 to 4.2.1.
- [Release notes](https://github.com/platformdirs/platformdirs/releases)
- [Changelog](https://github.com/platformdirs/platformdirs/blob/main/CHANGES.rst)
- [Commits](tox-dev/platformdirs@4.1.0...4.2.1)

---
updated-dependencies:
- dependency-name: platformdirs
  dependency-type: indirect
  update-type: version-update:semver-minor
...

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