Category Banners component not compatible with 3.2.0.beta2

@tgxworld thank you! I can confirm that the component is working again on my site running v3.2.0.beta2 :+1:

I wonder if you should edit the .discourse-compatibility file though. At the moment, anyone running versions between 3.1.999 and 3.2.0.beta2 will be given a version that depends on plugin API version 1.15.0. They should probably be pinned to 65a2cfc43fb5f6ffd2f8db3888552594ed21c501 instead (the commit before the refactor).