Bump nix from 0.23.0 to 0.23.1 (#4552)

Bumps [nix](https://github.com/nix-rust/nix) from 0.23.0 to 0.23.1.
- [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/v0.23.0...v0.23.1)

---
updated-dependencies:
- dependency-name: nix
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

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

polkadot/node/metrics/Cargo.toml

@@ -25,7 +25,7 @@ log = "0.4.13"
 
 [dev-dependencies]
 assert_cmd = "2.0.2"
-nix = "0.23.0"
+nix = "0.23.1"
 tempfile = "3.2.0"
 hyper = { version = "0.14.14", default-features = false, features = ["http1", "tcp"] }
 tokio = "1.13"