Update Rust crate hostname to 0.4

Author: oxide-renovate[bot]

Cargo.toml

@@ -52,7 +52,7 @@ slog-bunyan = "2.5"
 socket2 = { version = "0.5", features = ["all"] }
 ispf = { git = "https://github.com/oxidecomputer/ispf" }
 serde = { version = "1.0.219", features = ["derive"] }
-hostname = "0.3"
+hostname = "0.4"
 thiserror = "1.0"
 dropshot = { version = "0.16.2", features = [ "usdt-probes" ] }
 schemars = { version = "0.8", features = [ "uuid1", "chrono" ] }