erp5_project: allow to cancel a task report from the stopped state

bt5/erp5_project/WorkflowTemplateItem/portal_workflow/task_report_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>
                 <string>restart</string>