tests/unwrap-message-id.py

tests: fix command name in test-blackbox.t to be bytes

This command is only used when tests are run with --with-chg, so this was missed
before.

Differential Revision: https://phab.mercurial-scm.org/D7553

from __future__ import absolute_import, print_function

import re
import sys

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