Scrollbar is missing when editing category

[gerhard (Gerhard Schlager)]

When you edit a category it’s not possible to scroll on the settings tab anymore. Looks like it’s caused by select-box-kit which adds overflow: hidden to the .modal-body element.

https://github.com/discourse/discourse/blob/master/app/assets/javascripts/select-box-kit/mixins/dom-helpers.js.es6#L185

cc @joffreyjaffeux