Don't block when emitting fs events

Blocking could happen while processing events, which would cause the
background scanner to never make any further progress.

crates/project/src/worktree.rs

@@ -386,7 +386,7 @@ impl Worktree {
                     if worktree.poll_task.is_none() {
                         worktree.poll_task = Some(cx.spawn(|this, mut cx| async move {
                             if is_fake_fs {
-                                smol::future::yield_now().await;
+                                cx.background().simulate_random_delay().await;
                             } else {
                                 smol::Timer::after(Duration::from_millis(100)).await;
                             }