Update 2d_sprite_animation.rst

Corrected the C# code from the example in the 'Controlling the animation' section, fixing the class name used by the generic method GetNode<T>(), as well as the string parameter.

tutorials/2d/2d_sprite_animation.rst

@@ -101,7 +101,7 @@ released.
 
         public override void _Ready()
         {
-            _animatedSprite = GetNode<AnimatedSprite>("AnimatedSprite");
+            _animatedSprite = GetNode<AnimatedSprite2D>("AnimatedSprite2D");
         }
 
         public override _Process(float _delta)