lnrpc: log channel point in coop close warning

Use `Warnf` to include the chanpoint in the warning message instead of printing `%v` to the log

rpcserver.go

@@ -3309,7 +3309,7 @@ func (r *rpcServer) PendingChannels(ctx context.Context,
 		// state. We log a warning that the channel will not be included
 		// in the now deprecated pending close channels field.
 		case channeldb.CooperativeClose:
-			rpcsLog.Warn("channel %v cooperatively closed and "+
+			rpcsLog.Warnf("channel %v cooperatively closed and "+
 				"in pending close state",
 				pendingClose.ChanPoint)