Use forked version of postgres 8 to avoid Docker image format version issues.

See: https://docs.docker.com/engine/deprecated/#pushing-and-pulling-with-image-manifest-v2-schema-1

Forked images created by pulling the original image and pushing to the fork. For more details, see: https://github.com/golang-migrate/migrate/pull/1143#issuecomment-2328069381