The _ssh-host-certs.target_ unit does not exist any more. It was
provided by the _sshca-cli-systemd_ package to allow machines to
automatically request their SSH host certificates on first boot. It had
a `ConditionFirstBoot=` requirement, which made it not work at any other
time, so there was no reason to move it into the Ansible configuration
policy. Instead, we can use the _ssh-host-certs-renew.target_ unit to
trigger requesting or renewing host certificates.