Libimagequant is dual-licensed:

• For Free/Libre Open Source Software it's available under GPL v3 or later with additional [copyright notices] (https://raw.github.com/ImageOptim/libimagequant/master/COPYRIGHT) for historical reasons.
• For use in closed-source software, AppStore distribution, and other non-GPL uses, you can obtain a commercial license. Feel free to ask kornel@pngquant.org for details and custom licensing terms if you need them.

If I use libimagequant in my Open Source Software, and also publish it to AppStore, users can download it either from github's releases page or from AppStore, what type of license should it has?