Alerting: Fix ticker tests to not fail if channel is empty (#110538)

pkg/services/ngalert/schedule/ticker/ticker_test.go

@@ -30,8 +30,6 @@ func TestTicker(t *testing.T) {
 			return tick
 		case <-ctx.Done():
 			require.Failf(t, fmt.Sprintf("%v", ctx.Err()), "timeout reading the channel")
-		default:
-			require.Failf(t, "channel is empty but it should have a tick", "")
 		}
 		return time.Time{}
 	}