text_example_rs - cast check needs structural norm

https://crater-reports.s3.amazonaws.com/pr-133502-11/try%2328f13ad7c79d80decb5a3d54595a8b4105f397a3/gh/BsoftLimited.text_example_rs/log.txt

```rust
trait Mirror {
    type Assoc: ?Sized;
}
impl<T: ?Sized> Mirror for T {
    type Assoc = T;
}

struct W<'a>(&'a <[f32; 0] as Mirror>::Assoc);

fn foo(x: W<'_>) -> *const f32 {
    x.0 as *const f32
}

fn main() {}
```