Update Rust crate rustversion to 1.0.21

Author: oxide-renovate[bot]

Cargo.toml

@@ -13,7 +13,7 @@ quote = "1"
 syn = { version = "2", features = ["extra-traits", "derive"] }
 
 [dev-dependencies]
-rustversion = "1.0.20"
+rustversion = "1.0.21"
 serde = { version = "1.0.219", features = ["derive"] }
 serde_json = "1.0.140"
 trybuild = "1.0.104"