url_launcher_ios低版本强制修改extension UIApplication: Launcher

命令行：

code ~/.pub-cache/hosted/pub.flutter-io.cn/url_launcher_ios-6.2.4/ios/Classes/Launcher.swift

extension UIApplication: Launcher {
  @MainActor  // 添加 @MainActor 修饰符
  public func open(
    _ url: URL,
    options: [UIApplication.OpenExternalURLOptionsKey : Any] = [:],
    completionHandler: ((Bool) -> Void)? = nil
  ) {
    UIApplication.shared.open(url, options: options, completionHandler: completionHandler)
  }
}