Fix clippy error

Author: rylev

src/tools/clippy/tests/ui/crashes/ice-3969.stderr

@@ -5,18 +5,26 @@ LL |     for<'a> Dst<A + 'a>: Sized,
    |                 ^^^^^^ help: use `dyn`: `dyn A + 'a`
    |
    = note: `-D bare-trait-objects` implied by `-D warnings`
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2021 edition!
+   = note: for more information, see issue #80165 <https://github.com/rust-lang/rust/issues/80165>
 
 error: trait objects without an explicit `dyn` are deprecated
   --> $DIR/ice-3969.rs:27:16
    |
 LL |     let x: Dst<A> = *(Box::new(Dst { x: 1 }) as Box<Dst<A>>);
    |                ^ help: use `dyn`: `dyn A`
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2021 edition!
+   = note: for more information, see issue #80165 <https://github.com/rust-lang/rust/issues/80165>
 
 error: trait objects without an explicit `dyn` are deprecated
   --> $DIR/ice-3969.rs:27:57
    |
 LL |     let x: Dst<A> = *(Box::new(Dst { x: 1 }) as Box<Dst<A>>);
    |                                                         ^ help: use `dyn`: `dyn A`
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2021 edition!
+   = note: for more information, see issue #80165 <https://github.com/rust-lang/rust/issues/80165>
 
 error: aborting due to 3 previous errors