The world depicted on Apple TV+’s hit series “Severance” is already pretty bleak, but as it turns out, it could be even bleaker — all you need is the biggest jerk version of Stephen Colbert dropped into the madness.Colbert proved this on Thursday’s episode of “The Late Show” with a fun clip in which he becomes an employee of Lumen and we see what his workplace version is like. (The frame joke is that he actually did join the show, but all his scenes were cut, in case you’re curious.)Of course you know the premise, but for those who don’t, on “Severance,” the company Lumen has devised a procedure that allows people to literally separate their work and home lives completely.