c++ GDExtension how to get Autoload Global Data

### Godot version

4.3

### godot-cpp version

4.3

### System information

Window10 godot-cpp4.3

### Issue description

ERROR: Failed to retrieve non-existent singleton 'GlobalEcgResObj'.
at: (core/config/engine.cpp:294)


### Steps to reproduce

// 获取 GlobalEcgResObj 单例
Object *global_ecg_res_obj = Engine::get_singleton()->get_singleton("GlobalEcgResObj");

// 检查是否成功获取单例
if (global_ecg_res_obj) {
// 获取 check_uid 变量的值
Variant check_uid_variant = global_ecg_res_obj->get("check_uid");

// 转换为字符串类型
String check_uid_str = check_uid_variant.operator String();

// 打印输出
UtilityFunctions::print("check_uid: " + check_uid_str);
} else {
UtilityFunctions::print("Failed to GlobalEcgResObj singleton.");
}

### Minimal reproduction project

Failed to GlobalEcgResObj singleton.