tests/unwrap-message-id.py

run-tests: ensure the script exits when it fails to change directories

Caught by PyCharm as an unused variable assignment.  This regressed in
c496e8c14b9e.

Differential Revision: https://phab.mercurial-scm.org/D7750

from __future__ import absolute_import, print_function

import re
import sys

print(re.sub(r"(?<=Message-Id:) \n ", " ", sys.stdin.read()), end="")