fix scope in suppress dead_code (template) (#7532)

`#[allow(dead_code)]` -> `#![allow(dead_code)]` in templates

substrate/.maintain/frame-umbrella-weight-template.hbs

@@ -16,7 +16,7 @@
 #![allow(unused_parens)]
 #![allow(unused_imports)]
 #![allow(missing_docs)]
-#[allow(dead_code)]
+#![allow(dead_code)]
 
 use frame::weights_prelude::*;
 

substrate/.maintain/frame-weight-template.hbs

@@ -16,7 +16,7 @@
 #![allow(unused_parens)]
 #![allow(unused_imports)]
 #![allow(missing_docs)]
-#[allow(dead_code)]
+#![allow(dead_code)]
 
 use frame_support::{traits::Get, weights::{Weight, constants::RocksDbWeight}};
 use core::marker::PhantomData;