Update nix requirement from 0.22 to 0.23

Updates the requirements on [nix](https://github.com/nix-rust/nix) to permit the latest version.
- [Release notes](https://github.com/nix-rust/nix/releases)
- [Changelog](https://github.com/nix-rust/nix/blob/master/CHANGELOG.md)
- [Commits](https://github.com/nix-rust/nix/compare/v0.22.0...v0.23.1)

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

Signed-off-by: dependabot[bot] <support@github.com>

Cargo.toml

@@ -17,7 +17,7 @@ vm-memory = {version = "0.7", features = ["backend-mmap", "backend-atomic"]}
 vmm-sys-util = "0.9"
 
 [dev-dependencies]
-nix = "0.22"
+nix = "0.23"
 vhost = { version = "0.3", features = ["vhost-user-master", "vhost-user-slave"] }
 vm-memory = {version = "0.7", features = ["backend-mmap", "backend-atomic", "backend-bitmap"]}
 tempfile = "3.2.0"