tests: show unusual error message for `hg log --style coal`
It turns out that we show the full path when the given style name
matches a subdirectory of `mercurial/templates/`.
Differential Revision: https://phab.mercurial-scm.org/D8803
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}