build(deps): update nix requirement from 0.28.0 to 0.29.0 (#851)

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]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

poem/Cargo.toml

@@ -168,7 +168,7 @@ uuid = { version = "1.8.0", optional = true, default-features = false, features
 ] }
 
 [target.'cfg(unix)'.dependencies]
-nix = { version = "0.28.0", features = ["fs", "user"] }
+nix = { version = "0.29.0", features = ["fs", "user"] }
 
 [dev-dependencies]
 async-stream = "0.3.2"