Upgrade OS on dev.gitlab.org to Ubuntu 18.04 or 20.04
Part of gitlab-org&5109 (closed). Before we can stop building/publishing packages for Ubuntu 16.04, we should ensure none of our machines are still on Ubuntu 16.04. gitlab-com/gl-infra&231 exists for the GitLab.com fleet, but might not include dev.gitlab.org.
One thing to note, the fallback plan we are thinking of is to stop publishing 16.04 packages to users after April 2021. However, since dev.gitlab.org uses nightly packages, we might be able to keep nightly builds and pushes even after April 2021, until we get to dev.gitlab.org upgrade.
Edited by Balasankar 'Balu' C