Make compile error message point to field type instead of call site for not implemented Serialize trait

Author: Veetaha

test_suite/tests/ui/on-unimplemented/fn_param.rs

@@ -1,7 +1,6 @@
 use serde::de::Deserialize;
 use serde::ser::Serialize;
 
-
 fn to_string<T>(_: &T) -> String
 where
     T: Serialize,