tests: handle Message-Id line wrapping in test-notify-changegroup.t stable

tests: handle Message-Id line wrapping in test-notify-changegroup.t

This fixes this test on Python 3 with a long hostname. See changeset
4128ffba4431 for details.

--- a/tests/test-notify-changegroup.t	Sat Nov 02 12:09:35 2019 -0700
+++ b/tests/test-notify-changegroup.t	Mon Nov 04 09:35:10 2019 +0100
@@ -39,6 +39,7 @@
 push
 
   $ hg --traceback --cwd b push ../a 2>&1 |
+  >     "$PYTHON" $TESTDIR/unwrap-message-id.py | \
   >     "$PYTHON" -c 'from __future__ import print_function ; import sys,re; print(re.sub("\n\t", " ", sys.stdin.read()), end="")'
   pushing to ../a
   searching for changes
@@ -93,6 +94,7 @@
 unbundle with correct source
 
   $ hg --config notify.sources=unbundle --cwd a unbundle ../test.hg 2>&1 |
+  >     "$PYTHON" $TESTDIR/unwrap-message-id.py | \
   >     "$PYTHON" -c 'from __future__ import print_function ; import sys,re; print(re.sub("\n\t", " ", sys.stdin.read()), end="")'
   adding changesets
   adding manifests
@@ -169,6 +171,7 @@
 push
 
   $ hg --traceback --cwd b --config notify.fromauthor=True push ../a 2>&1 |
+  >     "$PYTHON" $TESTDIR/unwrap-message-id.py | \
   >     "$PYTHON" -c 'from __future__ import print_function ; import sys,re; print(re.sub("\n\t", " ", sys.stdin.read()), end="")'
   pushing to ../a
   searching for changes