tests/unwrap-message-id.py

run-tests: use byte strings for inserted output

We were inserting str on Python 3 which resulted in mixed
str/bytes types on the list. This would later blow up when
trying to write str to the .err file opened in bytes mode.

Differential Revision: https://phab.mercurial-scm.org/D7222

from __future__ import absolute_import, print_function

import re
import sys

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