Update nix requirement from 0.28.0 to 0.29.0

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@v0.28.0...v0.29.0)

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

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

Cargo.toml

@@ -69,7 +69,7 @@ unicode-linebreak = ">= 0.1.5" # Required to fix minimal-versions
 
 # For testing unix signals
 [target.'cfg(unix)'.dev-dependencies]
-nix = { version = "0.28.0", default-features = false, features = ["signal"] }
+nix = { version = "0.29.0", default-features = false, features = ["signal"] }
 
 # Make leak sanitizer more reliable
 [profile.dev]