Fix typo in game_menu.rs (bevyengine#4977)

Should be trivial

# Objective

There is a typo in a comment that is fixed in this commit

## Solution

Fix the typo
`positionned` -> `positioned`

---

examples/games/game_menu.rs

@@ -401,7 +401,7 @@ mod menu {
         };
         let button_icon_style = Style {
             size: Size::new(Val::Px(30.0), Val::Auto),
-            // This takes the icons out of the flexbox flow, to be positionned exactly
+            // This takes the icons out of the flexbox flow, to be positioned exactly
             position_type: PositionType::Absolute,
             // The icon will be close to the left border of the button
             position: UiRect {