Liza Minnelli is too short to ring the opening bell at the New York Stock Exchange. When she went yesterday morning to ring the bell with fellow amFar ambassador Cheyenne Jackson and amFar chairman Kenneth Cole, photographers on the trading floor couldn’t see the 5-foot, 4-inch legend above the podium. “They started screaming, ‘We can’t see! Put her on the box!’ Apparently they all knew there’s a box for short people on the stage near the podium,” said a spy. The platform gave Minnelli a 6-inch boost.