Fix tasks on wasm (#21096)

# Objective

Fix #21079. This was caused by incorrectly dropping a future.

## Solution

Await the future instead of dropping it.

## Testing

See
#21079 (comment).
@rparrett has indicated this resolves the issue. I have not personally
tested it.

We need to figure out a better solution to unit test the web. This would
be very easy to test, except that it requires `web_bindgen_futures` and
has to run in a browser environment.

Author: NthTensor

crates/bevy_tasks/src/task.rs

@@ -39,7 +39,7 @@ cfg::web! {
                     // Catch any panics that occur when polling the future so they can
                     // be propagated back to the task handle.
                     let value = CatchUnwind(AssertUnwindSafe(future)).await;
-                    let _ = sender.send(value);
+                    let _ = sender.send(value).await;
                 });
                 Self(receiver)
             }