Update nix requirement from 0.27 to 0.28

Updates the requirements on [nix](https://github.com/nix-rust/nix) to permit the latest version.
- [Changelog](https://github.com/nix-rust/nix/blob/master/CHANGELOG.md)
- [Commits](nix-rust/nix@v0.27.0...v0.28.0)

---
updated-dependencies:
- dependency-name: nix
  dependency-type: direct:production
...

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

Cargo.toml

@@ -14,7 +14,7 @@ rust-version = "1.60"
 
 [dependencies]
 comma = "1.0"
-nix = { version = "0.27", features = ["fs", "process", "signal", "term"] }
+nix = { version = "0.28", features = ["fs", "process", "signal", "term"] }
 regex = "1"
 tempfile = "3"
 thiserror = "1.0.34"