Refund part order but don’t refund shipping

at the moment I have a function which will refund the invoice on an order. However the shipping is currently also being refunded, which I don’t want.
Is there a way to set the shipping to zero on an invoice refund?

My code is currently this:

private function refundItems($order,$items) {
        $refundItems = $items;
        $items = [];

        foreach ($order->getAllVisibleItems() as $item) {
            if (!in_array($item->getId(), $refundItems)) {
                continue;
            }

            // create creditmemo item and add to array
            $creditmemoItem = $this->createCreditmemoItem($item);
            $items[] = $creditmemoItem;
        }
        
        // get the invoice id

        $invoiceId = null;

        foreach ($order->getInvoiceCollection() as $invoice) {
            // this will always point to the latest invoice id
            $invoiceId = $invoice->getId();
        }

        // refund the invoice
        $this->refundInvoice->execute(
            $invoiceId,
            $items,
            true, // false = offline / true = online
            true // notify customer
        );
    }

the refundInvoice uses the MagentoSalesApiRefundInvoiceInterface class.

So just to re-iterate, the partial refund works fine in the sense that, the individual items chosen are refunded but like I say, the shipping amount is also being refunded, which I don’t want to happen 🙂

Any help would be appreciated.

Cheers