message: locked_queue: robustify unit test against timeout
diff: @@ -91,10 +91,10 @@ TEST(LockedQueue, ConcurrantAccess)
  // The promise should not be fulfilled yet because we have not
  // returned the borrowed item.
  - auto status = fut.wait_for(std::chrono::milliseconds(10));
  + auto status = fut.wait_for(std::chrono::milliseconds(20));
  EXPECT_EQ(status, std::future_status::timeout);
  locked_queue.return_front();
  - status = fut.wait_for(std::chrono::milliseconds(10));
  + status = fut.wait_for(std::chrono::milliseconds(20));
  EXPECT_EQ(status, std::future_status::ready);
  }
  