graphmod: use raw string Needed to avoid a SyntaxWarning due to unescaped \ in Python 3.8. Differential Revision: https://phab.mercurial-scm.org/D5820

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