Corboy & Demetrio P.C. has a new managing partner for the first time in more than two decades: Kenneth T. Lumb.The firm’s last MP, Robert J. Bingle, stepped down from the role at the start of the year. He became the firm’s first managing partner in 1995, and he will remain a partner there.“I think he’ll do a wonderful job,” Bingle, 67, said of his successor. “I was honored to serve for …