build(deps): update nix requirement from 0.27.1 to 0.28.0

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@v0.27.1...v0.28.0)

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

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

poem/Cargo.toml

@@ -165,7 +165,7 @@ anyhow = { version = "1.0.0", optional = true }
 eyre06 = { package = "eyre", version = "0.6", optional = true }
 
 [target.'cfg(unix)'.dependencies]
-nix = { version = "0.27.1", features = ["fs", "user"] }
+nix = { version = "0.28.0", features = ["fs", "user"] }
 
 [dev-dependencies]
 async-stream = "0.3.2"