The final months of “The Late Show With Stephen Colbert” have followed a familiar script with a procession of celebrities getting a little sincere and paying tribute through sad songs and art projects. John Lithgow read a celebratory poem titled “The Mighty Colbert.” Jake Tapper brought a painting of the host as a version of Gollum from “The Lord of the Rings,” a Colbert obsession. Nathan Lane sang a ballad called “Laughing Matters.” Jimmy Fallon and Billy Crystal each gave their spin on