GitLab has moved to a new infrastructure on March 28th
As part of this migration, the SSH host keys were upgraded to stronger cryptographic standards. The first time you connect via SSH after the migration, you will see a warning like this:
WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!
This is expected: it does not indicate a security incident.
What to do?
Remove the old host key from your known hosts file by running ssh-keygen -R gitlab.switch.ch.
Your next SSH connection will prompt you to accept the new host key. Verify it matches one of the keys listed in: https://gitlab.switch.ch/help/instance_configuration