【Unity】CreateAssetMenu attribute on XXXX will be ignored as XXXX is not derived from ScriptableObject.

概要

CreateAssetMenu attribute on XXXX will be ignored as XXXX is not derived from ScriptableObject.
UnityEditor.AttributeHelper:ExtractCreateAssetMenuItems(Assembly)

ScriptableObject を継承していないクラスに CreateAssetMenu 属性を付与すると
上記の警告が発生します