Experiencing the same issue on Ubuntu 24.04 LTS with an omnibus installation (gitlab-ce). Upgradepath and procedures were followed. Gitlab was originally on 17.1.1 - > 17.3.7 → 17.5.3 → 17.6.0/17.6.1. Upgrade until 17.5.3 was working well, the upgrade to either 17.6.0 or 17.6.1 was always failing on this migration, regarding this
ALTER TABLE packages_dependencies VALIDATE CONSTRAINT check_83faf1f5e7;
Downgraded again, by restoring a backup, everything is working on 17.5.3 now again, but as soon as we want to upgrade to 17.6 it results in the same error.