我想用来do-release-upgrade从 18.04 升级到 20.04，但我不能这样做
do-release-upgrade
Checking for a new Ubuntu release
There is no development version of an LTS available.
好像用了这个文件，还是指向18.04。
你知道我什么时候（或如何？）可以升级到 20.04 吗？
$ sudo do-release-upgrade -c # It SHOULD work as 22.04 is released now
Checking for a new Ubuntu release
No new release found.
$ sudo do-release-upgrade -d # This is the only solution now which is abnormal
Checking for a new Ubuntu release
= Welcome to the Ubuntu 'Jammy Jellyfish' development release =
''This release is still in development.''
............
当前的镜像是archive.ubuntu.com. 当前的操作系统是21.10.