Bump nix from 0.20.0 to 0.20.2

Bumps [nix](https://github.com/nix-rust/nix) from 0.20.0 to 0.20.2.
- [Release notes](https://github.com/nix-rust/nix/releases)
- [Changelog](https://github.com/nix-rust/nix/blob/v0.20.2/CHANGELOG.md)
- [Commits](nix-rust/nix@v0.20.0...v0.20.2)

---
updated-dependencies:
- dependency-name: nix
  dependency-type: indirect
...

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