Students at a Manhattan Catholic elementary school were “devastated” to learn that their institution is one of three New York Archdiocese schools slated to shut down in June — leaving families with few other religious options to turn to. Incarnation School in Washington Heights broke the news to its community Monday as Catholic institutions continue to suffer plummeting enrollment and skyrocketing tuition. “I felt like it was blindsided. They had people coming in and out all year saying we were