我试图用SpirteKit创建一个无限的垂直滚动背景，但是我似乎不能让代码工作

import SpriteKit

class GameScene: SKScene {
    let background = SKSpriteNode(imageNamed: "background")
    
    override func didMove(to view: SKView) {
        // 设置背景图像的位置为屏幕中心
        background.position = CGPoint(x: size.width / 2, y: size.height / 2)
        
        // 创建滚动动作
        let scrollAction = SKAction.moveBy(x: 0, y: -size.height, duration: 5)
        let resetAction = SKAction.moveBy(x: 0, y: size.height, duration: 0)
        let sequence = SKAction.sequence([scrollAction, resetAction])
        let repeatAction = SKAction.repeatForever(sequence)
        
        // 应用滚动动作到背景图像
        background.run(repeatAction)
        
        // 将背景图像添加到场景中
        addChild(background)
    }
}