Adjust locator in billing test and add data-test attribute

Updated the locator for the 'manageBillingButton' in the end-to-end billing test. Instead of an id, the locator now targets a data property. This change was also reflected in the Button component within 'billing-portal-card.tsx' where the attribute data-test was added for test recognition.

packages/billing/gateway/src/components/billing-portal-card.tsx

@@ -27,7 +27,7 @@ export function BillingPortalCard() {
 
       <CardContent className={'space-y-2'}>
         <div>
-          <Button>
+          <Button data-test={'manage-billing-redirect-button'}>
             <span>
               <Trans i18nKey="billing:billingPortalCardButton" />
             </span>