backport unrecognized arguments
When pipelines are launched to update pkgs in v2020 (other releases are not affected), they fail with:
apertis-pkg-merge-upstream-to-downstreams: error: unrecognized arguments: --osname=... --stable=... --local-version-suffix=... --auto-merge=...
That happens because ci-package-builder.yml was updated to use new arguments for apertis-pkg-merge-upstream-to-downstreams that are not available in the docker image use to build pkgs for v2020.