Bump nix from 0.28.0 to 0.29.0

Bumps [nix](https://github.com/nix-rust/nix) from 0.28.0 to 0.29.0.
- [Changelog](https://github.com/nix-rust/nix/blob/master/CHANGELOG.md)
- [Commits](nix-rust/nix@v0.28.0...v0.29.0)

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

Signed-off-by: dependabot[bot] <[email protected]>