Rollup merge of #69128 - Centril:fix-69103, r=davidtwco

Rollup merge of #69128 - Centril:fix-69103, r=davidtwco

Fix extra subslice lowering

We are currently ICEing on e.g.
```rust
fn main() {
    let [.., b @ ..] = [1, 2];
    b;
}
```
This happens because `b @ ..` registers a binding such that `b;` is OK, but then we forget to lower that binding in `rustc_ast_lowering`.

Fixes #69103.

r? @davidtwco