build(deps): bump platformdirs from 3.6.0 to 3.8.0 in /nix

Bumps [platformdirs](https://github.com/platformdirs/platformdirs) from 3.6.0 to 3.8.0.
- [Release notes](https://github.com/platformdirs/platformdirs/releases)
- [Changelog](https://github.com/platformdirs/platformdirs/blob/main/CHANGES.rst)
- [Commits](tox-dev/platformdirs@3.6.0...3.8.0)

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

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