LOS ANGELES -- If leaving the storied role of “The Tonight Show” host mandates retirement, Jay Leno ignored the memo.Since his longtime late-night gig ended in 2014, Leno has kept up a brisk pace. He pops up regularly on TV projects from fellow comedians Jerry Seinfeld, Larry Wilmore, Tim Allen, Dennis Miller and others.His passion for anything with wheels and an engine is on display in “Jay Leno’s Garage,” returning Sept.