`User 'postgres' does not exist` error when postgres user does exist

[olirice]

We're currently adding plrust to the Supabase images and running into an install problem:

This line https://github.com/tcdi/plrust/blob/ca781d7e2ec75db0a26200b5e7e28e25ccaaa4df/.github/docker/Dockerfile.debian-artifact-build#L131-L134

returns exit code 1 even when the postgres user exists b/c the error code is not preserved