impl traits in consts through const fns are allowed but shouldn't

The following code compiles after #87141 but shouldn't

```rust
#![feature(const_impl_trait)]
#![feature(min_type_alias_impl_trait)]

type Foo = impl Send;

struct A;

const VALUE: Foo = value();

 const fn value() -> Foo {
     A
 }

fn main() {
}
```