Apple's long-rumored foldable iPhone — either called the iPhone Ultra or iPhone Fold, depending on which reports you go by — will likely be unveiled in just a few short weeks at the Apple September event. Over the weekend, a reputable leaker confirmed that September launch window, but warned that actually getting your hands on one around that time won't be easy.iPhone Ultra supply will be "extremely limited" when Apple unveils the foldable next month, according to Fixed Focus Digital, a noted Apple leaker on the Chinese social media platform Weibo (h/t 9to5Mac). Apple September 9 Event LEAKED! iPhone 18…