Change way of gettng Managers to use class name

UI/game_over_panel.gd

@@ -1,13 +1,11 @@
 extends Control
 
 @onready var _Restart_btn: Button = %Restart
-const GAME_MANAGER = preload("res://GameManager.gd")
-
 
 func _ready() -> void:
 	_Restart_btn.pressed.connect(_restart)
 	
 func _restart():
-	GAME_MANAGER._restart()
+	GameManager._restart()
 	get_tree().reload_current_scene()