NEW YORK — Nets star James Harden will miss his third straight game, against the Boston Celtics Tuesday, with left hamstring tightness. It is his fifth missed game due to injury in the team’s last seven outings and his fourth game missed because of his nagging left hamstring. Harden went through shootaround on Tuesday, then went to the weight room to workout. Veteran guard Patty Mills described his All-Star teammate as the “same-old, same-old James” on the floor, but when asked what Harden looked like in shootaround, DeAndre’ Bembry pumped the brakes. “I’m not sure how long he’s gonna be out, …