git-remote-mediawiki: fix incorrect test usage in test

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/mw-to-git/t/push-pull-tests.sh

@@ -104,7 +104,7 @@ test_push_pull () {
 			git push
 		) &&
 
-		test ! wiki_page_exist Foo
+		test_must_fail wiki_page_exist Foo
 	'
 
 	test_expect_success 'Merge conflict expected and solving it' '