[Typo] Tutorials -> Building 2D Games -> Chapter 11: Yellow Highlighting needed

In the "Updating the Game1 Class" region I believe there are some highlighting issues.

<img width="720" height="1175" alt="Image" src="https://github.com/user-attachments/assets/0ada048f-5351-4fa7-a5bb-8fd6b88e31c5" />