Don't show Extend Script option for built-in scripts

editor/scene_tree_dock.cpp

@@ -3792,7 +3792,7 @@ void SceneTreeDock::_tree_rmb(const Vector2 &p_menu_pos) {
 				menu->add_icon_shortcut(get_editor_theme_icon(SNAME("ScriptCreate")), ED_GET_SHORTCUT("scene_tree/attach_script"), TOOL_ATTACH_SCRIPT);
 			}
 
-			if (existing_script.is_valid()) {
+			if (existing_script.is_valid() && !existing_script->is_built_in()) {
 				menu->add_icon_shortcut(get_editor_theme_icon(SNAME("ScriptExtend")), ED_GET_SHORTCUT("scene_tree/extend_script"), TOOL_EXTEND_SCRIPT);
 			}
 		}