The mother of a Marine killed during the US’ botched withdrawal from Afghanistan on Saturday called “BS” on the fallen hero’s father getting arrested for heckling President Biden during his State of the Union address.“I was shocked because I thought it was complete BS that they arrested him,” Shana Chappell told The Post. “He shouldn’t have been arrested, he’s a Gold Star father. He’s in the same room as the man that he knows is responsible for our son’s death, so why was he arrested?”Chappell, 51, of Lake Elsinore, Calif., said she’s still struggling to survive nearly three years after...