swh-docker-dev CI build - broken since build #569 - 404 not found for psql apt repo

here's a recent failed build log

that's a weird one, the failure is:

Err:10 http://apt.postgresql.org/pub/repos/apt -pgdg/main amd64 Packages
  404  Not Found [IP: 217.196.149.55 80]
Fetched 7931 kB in 1s (6260 kB/s)
Reading package lists...
W: The repository 'http://apt.postgresql.org/pub/repos/apt -pgdg Release' does not have a Release file.
E: Failed to fetch http://apt.postgresql.org/pub/repos/apt/dists/-pgdg/main/binary-amd64/Packages  404  Not Found [IP: 217.196.149.55 80]
E: Some index files failed to download. They have been ignored, or old ones used instead.

looks like a malformed sources.list line, note the dists/-pgdg/main/ path aprt

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Migrated from T2644 (view on Phabricator)