Update Rust crate serde_with to 3.21.0

Author: renovate[bot]

Cargo.lock

@@ -43,7 +43,7 @@ salty = { version = "0.3", default-features = false }
 serde = { version = "1.0.228", default-features = false }
 serde-big-array = "0.5.1"
 serde_json = { version = "1.0.150", features = ["std", "alloc"] }
-serde_with = { version = "3.15.1", default-features = false }
+serde_with = { version = "3.21.0", default-features = false }
 serialport = { git = "https://github.com/jgallagher/serialport-rs", branch = "illumos-support" }
 sha2 = "0.11.0"
 sha3 = { version = "0.10.8", default-features = false }