Fix trivial numeric cast in visit_u64

serde_derive/src/de.rs

@@ -1428,7 +1428,7 @@ fn deserialize_identifier(
                     #variant_indices => _serde::export::Ok(#constructors),
                 )*
                 _ => _serde::export::Err(_serde::de::Error::invalid_value(
-                            _serde::de::Unexpected::Unsigned(__value as u64),
+                            _serde::de::Unexpected::Unsigned(__value),
                             &#fallthrough_msg))
             }
         }

test_suite/tests/test_macros.rs

@@ -6,6 +6,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![deny(trivial_numeric_casts)]
+
 #[macro_use]
 extern crate serde_derive;