By Zach Koons Without Kenny Pickett, Mike Tomlin will look down the depth chart for Sunday’s game. Mitch Trubisky will serve as the Steelers starting quarterback for Sunday’s game against the Panthers, the team announced Saturday afternoon. Mike Tomlin will turn to the former No. 2 pick once again after Pittsburgh officially ruled out rookie starter Kenny Pickett with a concussion. Pickett was forced to leave last weekend’s game against the Ravens after just two drives when his head hit the ground hard on a sack by Baltimore linebacker Roquan Smith. Trubisky, who started four games for the Ste…