gio/tests/task: fix for change to cancellation behavior

Multiple tasks cancelled at the same time now complete in the opposite
order from how they used to. Fix the test to not assume any particular
order.

gio/tests/task.c

@@ -1167,7 +1167,7 @@ test_run_in_thread_overflow (void)
   g_mutex_unlock (&overflow_mutex);
 
   /* Wait for all tasks to complete. */
-  while (!buf[NUM_OVERFLOW_TASKS - 1])
+  while (strlen (buf) != NUM_OVERFLOW_TASKS)
     g_usleep (1000);
 
   i = strspn (buf, ".");