Fix token bucket acquire

tokio/src/sync/semaphore.rs

@@ -292,8 +292,11 @@ use std::sync::Arc;
 ///
 /// async fn acquire(&self) {
 /// // This can return an error if the semaphore is closed, but we
-/// // never close it, so just ignore errors.
-/// let _ = self.sem.acquire().await;
+/// // never close it, so this error can never happen.
+/// let permit = self.sem.acquire().await.unwrap();
+/// // To avoid releasing the permit back to the semaphore, we use
+/// // the `Permit::forget` method.
+/// permit.forget();
 /// }
 /// }
 ///