fix: resolve issue where custom scenes created through a "createScene…

…s" message via the Mixer API SendInteractiveMessage would not be properly processed

Source/InteractiveSDK/Assets/MixerInteractive/Source/Scripts/InteractivityManager.cs

@@ -1758,7 +1758,7 @@ private void HandleSceneCreate(JsonReader jsonReader)
                     string keyValue = jsonReader.Value.ToString();
                     if (keyValue == WS_MESSAGE_KEY_SCENES)
                     {
-                        _scenes.Add(ReadScene(jsonReader));
+                        _scenes.AddRange(ReadScenes(jsonReader));
                     }
                 }
             }