Update ui test with diagnostic::on_unimplemented from PR 2767

test_suite/tests/ui/on_unimplemented.stderr

@@ -6,6 +6,8 @@ error[E0277]: the trait bound `MyStruct: Serialize` is not satisfied
  | |
  | required by a bound introduced by this call
  |
+ = note: for local types consider adding `#[derive(serde::Serialize)]` to your `MyStruct` type
+ = note: for types from other crates check whether the crate offers a `serde` feature flag
  = help: the following other types implement trait `Serialize`:
  &'a T
  &'a mut T
@@ -31,6 +33,8 @@ error[E0277]: the trait bound `MyStruct: Deserialize<'_>` is not satisfied
 22 | let _: MyStruct = from_str("");
  | ^^^^^^^^^^^^ the trait `Deserialize<'_>` is not implemented for `MyStruct`
  |
+ = note: for local types consider adding `#[derive(serde::Deserialize)]` to your `MyStruct` type
+ = note: for types from other crates check whether the crate offers a `serde` feature flag
  = help: the following other types implement trait `Deserialize<'de>`:
  &'a Path
  &'a [u8]