Properly support regions in overlap for negative impls

The following code should not compile but it does. This was noted in https://github.com/rust-lang/rust/pull/93175 where we know we are doing `predicate_must_hold_modulo_regions` but we shouldn't exactly do that.

```rust
trait Foo { }
impl !Foo for &'static () { }

trait Bar { }
#[rustc_strict_coherence]
impl<T: Foo> Bar for T { }
#[rustc_strict_coherence]
impl Bar for &() { }
```