sparse: fix debugrebuilddirsate when narrow extension is enabled
dirstate wrapping in narrow extension converts the manifest object to a list. So
let's assume we get a list of files in sparse extension.
Differential Revision: https://phab.mercurial-scm.org/D5481
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}