Enable Postgres 13
Since the time Postgres 13 came avaiable on Gentoo stable (even before fixing Postgres to 12 in the ebuild), I'm using Postgres 13 as DB-Backend for Gitlab and it works flawlessly. I think the Dep-Spec in the ebuild can be changed to postgres>=12. By doin so, nobody will be forced to use PG 13, but users can use it, if they desire to do so.