当我使用时sudo apt-get update && sudo apt-get upgrade，出现以下错误。
E: The repository 'http://old-releases.ubuntu.com/ubuntu bionic-old-releases Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default
N: See apt-secure(8) manpage for repository creation and user configuration details.
我尝试了一些解决方案，但似乎它们不适用于我的系统。我不知道如何更新/etc/apt/sources.list。