Back to Hogwarts is celebrated every year on September 1. This is the day that prospective Witches and Wizards board the Hogwarts Express, arrive at school, and enjoy a welcome feast alongside the Sorting Ceremony. For those not going to Hogwarts this year, the celebration is mostly about announcements and discounts on popular Potter merch.If you're in the market for the latter, there are a number of Harry Potter gifts on sale this week. I've gathered the best deals right…