test_atomic_wait.hpp: remove another timing assumption (#1193)

tests/std/include/test_atomic_wait.hpp

@@ -147,10 +147,14 @@ void test_pad_bits_impl(const std::chrono::steady_clock::duration waiting_durati
     c.store(new_value);
     c.notify_one();
 
+#ifdef CAN_FAIL_ON_TIMING_ASSUMPTION
     std::this_thread::sleep_for(waiting_duration);
     assert(trigger);
-
     w1.join();
+#else // ^^^ CAN_FAIL_ON_TIMING_ASSUMPTION / !CAN_FAIL_ON_TIMING_ASSUMPTION vvv
+    w1.join();
+    assert(trigger);
+#endif // ^^^ !CAN_FAIL_ON_TIMING_ASSUMPTION ^^^
 }
 
 template <class UnderlyingType>