在Ubuntu上安装GitLab:；无法解析主机：packages.gitlab.com“；

这是我的系统（新安装）：

我已经安装了OpenSSH和Postfix，并添加了GitLab存储库，但当我尝试安装GitLab时，我得到的是：

Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following NEW packages will be installed:
  gitlab-ce
0 upgraded, 1 newly installed, 0 to remove and 4 not upgraded.
Need to get 743 MB of archives.
After this operation, 1,961 MB of additional disk space will be used.
Err:1 https://packages.gitlab.com/gitlab/gitlab-ce/ubuntu xenial/main amd64 gitlab-ce amd64 12.8.1-ce.0
  Could not resolve host: packages.gitlab.com
E: Failed to fetch https://packages.gitlab.com/gitlab/gitlab-ce/ubuntu/pool/xenial/main/g/gitlab-ce/gitlab-ce_12.8.1-ce.0_amd64.deb  Could not resolve host: packages.gitlab.com

E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

我尝试了这两个建议，甚至尝试了更换网络，希望是学校的Wi-Fi。

首先尝试在浏览器中访问

如果这也失败了，则可能是域被防火墙阻止的情况

Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following NEW packages will be installed:
  gitlab-ce
0 upgraded, 1 newly installed, 0 to remove and 4 not upgraded.
Need to get 743 MB of archives.
After this operation, 1,961 MB of additional disk space will be used.
Err:1 https://packages.gitlab.com/gitlab/gitlab-ce/ubuntu xenial/main amd64 gitlab-ce amd64 12.8.1-ce.0
  Could not resolve host: packages.gitlab.com
E: Failed to fetch https://packages.gitlab.com/gitlab/gitlab-ce/ubuntu/pool/xenial/main/g/gitlab-ce/gitlab-ce_12.8.1-ce.0_amd64.deb  Could not resolve host: packages.gitlab.com

E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?