Linux下不能连接ppa.launchpad.net的问题（中科大软件源）

/etc/apt/sources.list.d/borglab-ubuntu-gtsam-release-4_0-focal.list

http://ppa.launchpad.net=>https://launchpad.proxy.ustclug.org

#deb http://ppa.launchpad.net/borglab/gtsam-release-4.0/ubuntu focal main
deb https://launchpad.proxy.ustclug.org/borglab/gtsam-release-4.0/ubuntu focal main