Convert "! git" to "test_must_fail git"

test_must_fail will account for segfaults in git, so it should be used
instead of "! git"

This patch does not change any of the commands that use pipes.

Signed-off-by: Jared Hance <jaredhance@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t9139-git-svn-non-utf8-commitencoding.sh b/t/t9139-git-svn-non-utf8-commitencoding.sh
index f337959..22d80b0 100755
--- a/t/t9139-git-svn-non-utf8-commitencoding.sh
+++ b/t/t9139-git-svn-non-utf8-commitencoding.sh
@@ -39,7 +39,7 @@
 	(
 		cd $H &&
 		git config --unset i18n.commitencoding &&
-		! git svn dcommit
+		test_must_fail git svn dcommit
 	)
 	'
 done