.arcconfig

windows: open registry keys using unicode names

Python3 complained it must be str.  While here, use a context manager to close
the key- it wouldn't wrap at 80 characters the old way, and would have had to
move anyway.

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