I ran into the same problem.
Naively, I thought rebuilding my container would fix it, but in the current Discourse, Postgres is still at 15.12.
I was able to restore after a manual apt update / apt upgrade inside my container, but this feels quite hacky.
Did I miss something?
Do you have separate data and web only containers?
Do you somehow have docker_manager pinned to an old version?
Are you using an external postgres?
Thanks for the pointer. This was the case.
I changed a template and did a local commit, which did not merge automatically.
You should just copy your new template somewhere else and refer to it rather than editing it.