3D Game: Fix text to reflect the context images for collision masks (#4578)

Co-authored-by: Hugo Locurcio <[email protected]>

getting_started/first_3d_game/06.jump_and_squash.rst

@@ -85,8 +85,8 @@ Select the *Player* node and set its *Collision -> Mask* to both "enemies" and
 Then, open the *Mob* scene by double-clicking on ``Mob.tscn`` and select the
 *Mob* node.
 
-Set its *Collision -> Layer* to "enemies" and its *Collision -> Mask* to both
-"player".
+Set its *Collision -> Layer* to "enemies" and unset its *Collision -> Mask*,
+leaving the mask empty.
 
 |image6|