Bump nix from 0.19.1 to 0.20.0 (#3587)

Bumps [nix](https://github.com/nix-rust/nix) from 0.19.1 to 0.20.0.
- [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/v0.19.1...v0.20.0)

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

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

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

polkadot/Cargo.lock

@@ -4403,9 +4403,9 @@ dependencies = [
 
 [[package]]
 name = "nix"
-version = "0.19.1"
+version = "0.20.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b2ccba0cfe4fdf15982d1674c69b1fd80bad427d293849982668dfe454bd61f2"
+checksum = "fa9b4819da1bc61c0ea48b63b7bc8604064dd43013e7cc325df098d49cd7c18a"
 dependencies = [
  "bitflags",
  "cc",

polkadot/Cargo.toml

@@ -18,7 +18,7 @@ parity-util-mem = { version = "*", default-features = false, features = ["jemall
 
 [dev-dependencies]
 assert_cmd = "1.0.2"
-nix = "0.19.1"
+nix = "0.20.0"
 tempfile = "3.2.0"
 
 [workspace]