Missing warning for an unused const in async fn

I tried this code:

```rust
pub async fn foo() {
    const A: usize = 1;
}
```

I expected to see the warning:
> warning: constant `A` is never used

Instead no warning was reported by the compiler.

Observed in nightly, 1.67.
Seems like the warning was shown in 1.63 and stopped showing in 1.64.