Fixed suffix declaration in XSD
Fixed suffix declaration in XSD

As of now, a suffix is only allowed for option categories, which is wrong,
because a suffix can only be applied to an option itself.

Resolves #4596

SoftCreatR/WCF,WoltLab/WCF,WoltLab/WCF,SoftCreatR/WCF,SoftCreatR/WCF,SoftCreatR/WCF,WoltLab/WCF,WoltLab/WCF