Ignore flaky test (#6767)

substrate/client/network/src/service/tests.rs

@@ -345,7 +345,9 @@ fn lots_of_incoming_peers_works() {
 	});
 }
 
+// TODO: this test is at the moment ignored because of https://github.com/paritytech/substrate/issues/6766
 #[test]
+#[ignore]
 fn notifications_back_pressure() {
 	// Node 1 floods node 2 with notifications. Random sleeps are done on node 2 to simulate the
 	// node being busy. We make sure that all notifications are received.