ices/69307.rs: fixed with no errors

[github-actions]

Issue: rust-lang/rust#69307

fn block_on<F>(_: F) -> usize {
    0
}

fn main() {
    let mut sum = 0;
    sum += block_on(async {
        (async {}).await;
        1
    });
}

=== stdout ===
=== stderr ===
warning: variable `sum` is assigned to, but never used
 --> /home/runner/work/glacier/glacier/ices/69307.rs:6:13
  |
6 |     let mut sum = 0;
  |             ^^^
  |
  = note: `#[warn(unused_variables)]` on by default
  = note: consider using `_sum` instead

warning: value assigned to `sum` is never read
 --> /home/runner/work/glacier/glacier/ices/69307.rs:7:5
  |
7 |     sum += block_on(async {
  |     ^^^
  |
  = note: `#[warn(unused_assignments)]` on by default
  = help: maybe it is overwritten before being read?

==============