merge hook tests: fix missing '&&' in test

Signed-off-by: Benoit Pierre <benoit.pierre@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7505-prepare-commit-msg-hook.sh

@@ -174,7 +174,7 @@ test_expect_success 'with failing hook (merge)' '
 	git add file &&
 	rm -f "$HOOK" &&
 	git commit -m other &&
-	write_script "$HOOK" <<-EOF
+	write_script "$HOOK" <<-EOF &&
 	exit 1
 	EOF
 	git checkout - &&