test-check-py3-compat: remove false output from "python3 check-py3-compat.py" If python3 were python2, these errors would be reported, but we're running check-py3-compat.py on Python 3 here.

{
    "conduit_uri": "https://phab.mercurial-scm.org/api",
    "repository.callsign": "HG",
    "arc.land.onto.default": "@",
    "base": "hg:.^"
}