tests: improve portability by no longer using the flag [tar --force-local]
A different way of making sure the path is not interpreted as a URL is to never
give this path to [tar], instead making tar read from stdin.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}