test: Disable flaky test (#3555)

This disables the flaky test mentioned in #3401, since we don't have a
solution for it yet and it interrupts the normal flow of the pipeline.

Author: spydon

packages/flame/test/collisions/collision_type_test.dart

@@ -173,6 +173,9 @@ void main() {
         expect(blockB.activeCollisions.length, 0);
       },
       'correct collisions with many involved collidables': (game) async {
+        // Skip this test until it can be made non-flaky.
+        return;
+        // ignore: dead_code
         final rng = Random(0);
         List<TestBlock> generateBlocks(CollisionType type) {
           return List.generate(