Note that the lint for un-awaited Future doesn't mention the way to silence them by assigning to _:

  warning: unused implementer of `Future` that must be used
   --> src/main.rs:9:5
    |
  9 |     foo();
    |     ^^^^^
    |
    = note: futures do nothing unless you `.await` or poll them
    = note: `#[warn(unused_must_use)]` on by default