ERP5Workflow: declare execute WorkflowScript method as public

this is a wrapper for the PythonScript __call__ method
It should fix testSecurity

product/ERP5Workflow/Document/WorkflowScript.py

@@ -52,6 +52,7 @@ class WorkflowScript(PythonScript, IdAsReferenceMixin("script_", "prefix")):
                       , PropertySheet.PythonScript
                       )
 
+  security.declarePublic("execute")
   execute = PythonScript.__call__
 
 InitializeClass(WorkflowScript)