py3: use bytes stdout in test-check-help.t
Setting stdout to binary seemed to have no effect on Windows, as it was
appending a literal '\r' to each topic keyword. This also stops prepending 'b'
to the topic on all platforms as well.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}