Improve debug_handler message for generic request-consuming extractors (#1826)

Co-authored-by: David Pedersen <[email protected]>

axum-macros/tests/debug_handler/fail/json_not_deserialize.rs

@@ -0,0 +1,9 @@
+use axum::Json;
+use axum_macros::debug_handler;
+
+struct Struct {}
+
+#[debug_handler]
+async fn handler(foo: Json<Struct>) {}
+
+fn main() {}