build(deps): bump the vhost group with 1 update

Updates the requirements on [nix](https://github.com/nix-rust/nix) to permit the latest version.

Updates `nix` to 0.28.0
- [Changelog](https://github.com/nix-rust/nix/blob/master/CHANGELOG.md)
- [Commits](https://github.com/nix-rust/nix/compare/v0.27.0...v0.28.0)

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

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

vhost-user-backend/Cargo.toml

@@ -23,7 +23,7 @@ vm-memory = { version = "0.14.0", features = ["backend-mmap", "backend-atomic"]
 vmm-sys-util = "0.12.1"
 
 [dev-dependencies]
-nix = { version = "0.27", features = ["fs"] }
+nix = { version = "0.28", features = ["fs"] }
 vhost = { path = "../vhost", version = "0.10", features = ["test-utils", "vhost-user-frontend", "vhost-user-backend"] }
 vm-memory = { version = "0.14.0", features = ["backend-mmap", "backend-atomic", "backend-bitmap"] }
 tempfile = "3.2.0"