Ariana Grande and Ethan Slater are feeling more comfortable having public date nights as the holiday season goes on. Grande and Slater went to see Gutenberg! The Musical on Sunday, with star Andrew Rannells sharing a photo of Slater and Grande alongside him and co-star Josh Gad backstage. “We had some big fun in Schlimmer yesterday!” Rannells wrote. “Spamalot’s Ethan …