deps(rust): update hostname requirement from ^0.3.1 to ^0.4.0

Updates the requirements on [hostname](https://github.com/svartalf/hostname) to permit the latest version.
- [Release notes](https://github.com/svartalf/hostname/releases)
- [Changelog](https://github.com/svartalf/hostname/blob/master/CHANGELOG.md)
- [Commits](svartalf/hostname@v0.3.1...v0.4.0)

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

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

Cargo.toml

@@ -28,7 +28,7 @@ tracing = "^0.1.37"
 urlencoding = "2.1.3"
 uuid = { version = "^1.4.1", features = [ "v4", "serde" ] }
 os-release = "^0.1.0"
-hostname = "^0.3.1"
+hostname = "^0.4.0"
 openssl = "^0.10.55"
 compact_jwt = { version = "0.3.5", optional = true }
 kanidm-hsm-crypto = { version = "^0.2.0", optional = true }