test/CodingStyle: add exceptional prefix `Brain`

This is for catalog brain displayed in Listbox.

product/ERP5Type/CodingStyle.py

@@ -80,6 +80,7 @@ def getSkinPrefixList(self):
 
     'Entity', # A base class for Person / Organisation
     'Form', # Acceptable for ERP5 Forms which will soon become portal types too
+    'Brain', # Catalog brains
   ))
 
   return set(skin_prefix_list)