.arcconfig

fix: disable use of thread-based worker

getfixes() accesses to repo, changectx, filectx, etc., so I believe there
are code paths triggering data race. Mercurial API isn't thread safe in
general.

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