tests: always access the mercurial repo through `helpers-testrepo.sh`
In some contexts the mercurial repo needs to be accessed through system hg.
That's what `helpers-testrepo.sh` enforces, but some tests incorrectly
use the mercurial repo without going through that script.
This patch fixes those tests.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}