test: make sure sparse-revlog does not interfer with test-parseindex.t
That test carefully craft revlog to reproduce issues. We do not want new revlog
behavior to interfere with that.
Differential Revision: https://phab.mercurial-scm.org/D5314
{
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"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}