fix: CameraComponent no longer throws Concurrent modification on stop

.github/.cspell/gamedev_dictionary.txt

@@ -46,6 +46,7 @@ raytracing # rendering techniques that calculates light rays as straight lines
 rects # plural of rect
 respawned # past tense of respawn
 respawn # when the player character dies and is brought back after some time and penalties
+retarget # to direct (something) toward a different target
 RGBA # red green blue alpha
 RGBO # red green blue opacity
 rrect # rounded rect

packages/flame/lib/src/camera/camera_component.dart

@@ -323,7 +323,7 @@ class CameraComponent extends Component {
 
   /// Removes all movement effects or behaviors from the viewfinder.
   void stop() {
-    viewfinder.children.forEach((child) {
+    viewfinder.children.toList().forEach((child) {
       if (child is FollowBehavior || child is MoveEffect) {
         child.removeFromParent();
       }

packages/flame/test/camera/camera_component_test.dart

@@ -60,6 +60,20 @@ void main() {
       }
     });
 
+    testWithFlameGame('camera should be able to retarget follow', (game) async {
+      // Creating new camera as the one included with game is not mounted and
+      // will therefore not be queued.
+      final camera = CameraComponent(world: game.world)..addToParent(game);
+      final player = PositionComponent()..addToParent(game.world);
+      final player2 = PositionComponent()..addToParent(game.world);
+      camera.follow(player);
+      camera.follow(player2);
+      await game.ready();
+
+      expect(camera.viewfinder.children.length, 1);
+      expect(camera.viewfinder.children.first, isA<FollowBehavior>());
+    });
+
     testWithFlameGame('follow with snap', (game) async {
       final world = World()..addToParent(game);
       final player = PositionComponent()