tests/elm: add explicit printf for event cb assert failure

efl explodes when this assert fails and presents bizarre errors which
obscure the actual test failure, so add a more explicit message as a
reminder to check this instead of trying to dive into insanity

Differential Revision: https://phab.enlightenment.org/D11238

src/tests/elementary/suite_helpers.c

@@ -598,6 +598,7 @@ event_callback_single_call_int_data(void *data, Evas_Object *obj EINA_UNUSED, vo
 {
    int *called = data;
 
+   if (*called) fprintf(stderr, "TEST FAILURE IN %s\n", __func__);
    ck_assert_int_eq(*called, 0);
    *called = 1;
 }