[deps]: Update Rust crate darling to 0.21.0

Author: renovate[bot]

crates/bitwarden-error-macro/Cargo.toml

@@ -18,7 +18,7 @@ keywords.workspace = true
 wasm = []
 
 [dependencies]
-darling = "0.20.10"
+darling = "0.21.0"
 proc-macro2 = { workspace = true }
 quote = { workspace = true }
 syn = { workspace = true }