error[E0751]: found both positive and negative implementation of trait `DerefMut` for type `&MyType<'_>`:
  --> $DIR/pin-unsound-issue-66544-derefmut.rs:12:1
   |
LL | impl<'a> DerefMut for &'a MyType<'a> {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ positive implementation here
   |
   = note: negative implementation in crate `core`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0751`.