[BUG] compose config reports a default network even if not needed

[luciangabor]

$ docker compose -f - config <<-'EOF'
name: oh-no
services:
  service:
    image: image
    networks:
      net:
networks:
  net:
EOF
name: oh-no
networks:
  default:
    name: oh-no_default
  net:
    name: oh-no_net
services:
  service:
    image: image
    networks:
      net: null

(up doesn't create it)

#11587 (comment)
#11589 (comment)

[ndeloof]

fixed by #11604 and compose-spec/compose-go#595