The staffers who resigned worked for what was once known as the United States Digital Service and announced their departure through a joint resignation letter. WASHINGTON — More than 20 civil service employees resigned Tuesday from billionaire Trump adviser Elon Musk's Department of Government Efficiency, saying they were refusing to use their technical expertise to “dismantle critical public services.” “We swore to serve the American people and uphold our oath to the Constitution across presidential administrations,” the 21 staffers wrote in a joint resignation letter, a copy of which was obtained by The Associated Press. “However, it has become clear…