ices/86535.rs: fixed with errors

[github-actions]

Issue: rust-lang/rust#86535

#![feature(box_syntax)]
fn main() {
    let _: Box<[isize]> = box { loop {} };
}

=== stdout ===
=== stderr ===
warning: unreachable expression
 --> /home/runner/work/glacier/glacier/ices/86535.rs:3:27
  |
3 |     let _: Box<[isize]> = box { loop {} };
  |                           ^^^^^^-------^^
  |                           |     |
  |                           |     any code following this expression is unreachable
  |                           unreachable expression
  |
  = note: `#[warn(unreachable_code)]` on by default

error[E0277]: the size for values of type `[isize]` cannot be known at compilation time
 --> /home/runner/work/glacier/glacier/ices/86535.rs:3:31
  |
3 |     let _: Box<[isize]> = box { loop {} };
  |                               ^^^^^^^^^^^ doesn't have a size known at compile-time
  |
  = help: the trait `Sized` is not implemented for `[isize]`
  = note: the type of a box expression must have a statically known size

error: aborting due to previous error; 1 warning emitted

For more information about this error, try `rustc --explain E0277`.
==============