Make unbounded channels size warning exact (part 2) (#13504)

substrate/client/utils/src/notification.rs

@@ -79,7 +79,7 @@ impl<Payload, TK: TracingKeyStr> NotificationStream<Payload, TK> {
 	}
 
 	/// Subscribe to a channel through which the generic payload can be received.
-	pub fn subscribe(&self, queue_size_warning: i64) -> NotificationReceiver<Payload> {
+	pub fn subscribe(&self, queue_size_warning: usize) -> NotificationReceiver<Payload> {
 		let receiver = self.hub.subscribe((), queue_size_warning);
 		NotificationReceiver { receiver }
 	}