Fix attr accesses on msg type

piker/brokers/ib.py

@@ -1399,7 +1399,7 @@ async def trades_dialogue(
                 # it's a trade event generated by TWS usage.
                 log.warning(f"TWS triggered trade:\n{pformat(msg)}")
 
-                msg['reqid'] = 'tws-' + str(-1 * msg['reqid'])
+                msg.reqid = 'tws-' + str(-1 * msg.reqid)
 
                 # mark msg as from "external system"
                 # TODO: probably something better then this.. and start