tests: `hg init` after resetting HGRCPATH
Otherwise extensions loaded via --extra-config-opt could prevent
access to the repo by introducing requirements file. This does mean
that custom extensions loaded in this way won't impact this test.
I'm fine with that.
Differential Revision: https://phab.mercurial-scm.org/D3115
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}