Another tiny fix for `ExecutionManager.execution_from_child_message`

shared/workspaces/workspaces/capability/services/execution_manager.py

@@ -198,6 +198,7 @@ class ExecutionManager(ExecutionManagerIF):
         :return: CapabilityExecution if one can be located for child request; else None
         """
         msg_subject = message.get("subject")
+        parent_wf_request_id = None
 
         if msg_subject.get("execution_wf_id"):
             parent_wf_request_id = msg_subject.get("execution_wf_id")