[问题解决：Failed to download metadata for repo ‘appstream‘: Cannot prepare internal mirrorlist:...](%E9%97%AE%E9%A2%98%E8%A7%A3%E5%86%B3%EF%BC%9AFailedtodownloadmetadataforrepo%E2%80%98appstream%E2%80%98Cannotprepareinternalmirrorlist....md)