fix: Add missing generic to ComponentViewportMargin (#2983)

Improve `ComponentViewportMargin` (see #2982)


Closes #2982

packages/flame/lib/src/components/mixins/component_viewport_margin.dart

@@ -1,6 +1,7 @@
 import 'package:flame/camera.dart';
 import 'package:flame/components.dart';
 import 'package:flame/effects.dart';
+import 'package:flame/src/game/flame_game.dart';
 import 'package:flutter/widgets.dart' show EdgeInsets;
 import 'package:meta/meta.dart';
 
@@ -19,7 +20,8 @@ import 'package:meta/meta.dart';
 /// Do note that this only works with the old style camera and not the
 /// [CameraComponent].
 // TODO(Lukas): Rename this since it isn't necessarily related to the viewport.
-mixin ComponentViewportMargin on PositionComponent, HasGameReference {
+mixin ComponentViewportMargin<T extends FlameGame>
+    on PositionComponent, HasGameReference<T> {
   /// Instead of setting a position of the [PositionComponent] that uses
   /// [ComponentViewportMargin] a margin from the edges of the parent can be
   /// used instead.

packages/flame/test/components/mixins/component_viewport_margin_test.dart

@@ -1,12 +1,14 @@
 import 'package:flame/components.dart';
+import 'package:flame/game.dart';
 import 'package:flame_test/flame_test.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
   group('ComponentViewportMargin', () {
-    testWithFlameGame(
+    testWithGame(
       'margin should stay same after GameResize',
+      _TestGame.new,
       (game) async {
         final initialGameSize = Vector2.all(100);
         final componentSize = Vector2.all(10);
@@ -40,5 +42,7 @@ void main() {
   });
 }
 
+class _TestGame extends FlameGame<World> {}
+
 class _ComponentWithViewportMargin extends PositionComponent
-    with HasGameReference, ComponentViewportMargin {}
+    with HasGameReference<_TestGame>, ComponentViewportMargin<_TestGame> {}