tests: make sure input to sed is newline terminated

tests: make sure input to sed is newline terminated

POSIX only requires sed to work on text files and because it does
not end with a newline, this commit's content is not a text file.
Add a newline to fix it.  Without this change, OS X sed helpfully
adds a newline to actual.message, causing t9010.13 to fail.

Reported-by: Torsten Bögershausen <tboegi@web.de>
Tested-by: Brian Gernhardt <benji@silverinsanity.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>