BOSTON — A judge on Massachusetts' highest court is stepping into a fight over the proposed sale of works of art by a cash-strapped museum.A hearing before a single justice of the Supreme Judicial Court is set for Tuesday in Boston.The Berkshire Museum and Attorney General Maura Healey last month asked the judge to sign off on an agreement that would allow the Pittsfield museum to sell up to 40 pieces of art, including works by Norman Rockwell.The museum says it needs to sell the art to keep its doors open.