Update test/game/components/spaceship_exit_rail_test.dart

Co-authored-by: Alejandro Santiago <dev@alestiago.com>

test/game/components/spaceship_exit_rail_test.dart

@@ -31,6 +31,8 @@ void main() {
       when(() => fixture.filterData).thenReturn(filterData);
     });
 
+   // TODO(alestiago): Make ContactCallback private and use `beginContact`
+   // instead.
     group('SpaceshipExitHoleBallContactCallback', () {
       setUp(() {
         when(() => ball.priority).thenReturn(1);