tests: pass re.MULTILINE to re.sub as 'flags' - not in 'count' position
This bug was caught by the new Python 3.13 warning:
DeprecationWarning: 'count' is passed as positional argument
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"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}