erp5_trade: It is possible to cancel a Packing List after Shipping

bt5/erp5_trade/WorkflowTemplateItem/portal_workflow/packing_list_workflow/states/started.xml

@@ -28,6 +28,8 @@
             <key> <string>transitions</string> </key>
             <value>
               <tuple>
+                <string>cancel</string>
+                <string>cancel_action</string>
                 <string>deliver</string>
                 <string>deliver_action</string>
                 <string>stop</string>

bt5/erp5_trade/WorkflowTemplateItem/portal_workflow/packing_list_workflow/states/stopped.xml

@@ -28,6 +28,8 @@
             <key> <string>transitions</string> </key>
             <value>
               <tuple>
+                <string>cancel</string>
+                <string>cancel_action</string>
                 <string>deliver</string>
                 <string>deliver_action</string>
               </tuple>