error: this `Deref` implementation is covered by an implicit supertrait coercion
  --> $DIR/migrate-lint-deny.rs:9:1
   |
LL | impl<'a> Deref for dyn 'a + B {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `dyn B` implements `Deref<Target = dyn A>` which conflicts with supertrait `A`
...
LL |     type Target = dyn A;
   |     -------------------- target type is a supertrait of `dyn B`
   |
   = warning: this will change its meaning in a future release!
   = note: for more information, see issue #89460 <https://github.com/rust-lang/rust/issues/89460>
note: the lint level is defined here
  --> $DIR/migrate-lint-deny.rs:1:9
   |
LL | #![deny(deref_into_dyn_supertrait)]
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 1 previous error