“This isn’t a vacation. It’s a quarantine,” Bethlehem Million (“Flatbush Misdemeanors”) reminds Gideon Adlon (“Blockers”) in a new trailer for “Sick.” The pandemic-themed horror pic is set in April 2020 and follows two friends (Million and Adlon) who decide to quarantine at a family lake house. “The only neighbor is miles away,” we’re told. The…