Since 2016, Joe Keery has been mostly known as Steve Harrington, the bully-turned-beloved sentimental anchor on “Stranger Things,” who, no matter how many Demogorgons he’s fought, still has great hair. But you wouldn’t know it if you turned on the latest season of FX’s “Fargo.” Keery, sporting a buzz cut and shades, embodies a dangerous and edgy demeanor — yet, still charming…