docs: Fix typo in TextComponent sample code (#2910)

This changed `=` to `:` when calling named parameter `position`.

Co-authored-by: Lukas Klingsbo <me@lukas.fyi>

doc/flame/rendering/text_rendering.md

@@ -29,7 +29,7 @@ class MyGame extends FlameGame {
     add(
       TextComponent(
         text: 'Hello, Flame',
-        position = Vector2.all(16.0),
+        position: Vector2.all(16.0),
       ),
     );
   }