Fix stripe SCA redirect/sandboxing

src/pretix/plugins/stripe/static/pretixplugins/stripe/pretix-stripe.js

@@ -295,6 +295,7 @@ var pretixstripe = {
             let iframe = document.createElement('iframe');
             iframe.src = payment_intent_next_action_redirect_url;
             iframe.className = 'embed-responsive-item';
+            iframe.setAttribute('sandbox', 'allow-top-navigation');
             $('#scacontainer').append(iframe);
             $('#scacontainer iframe').on("load", function () {
                 waitingDialog.hide();
@@ -430,4 +431,4 @@ $(function () {
             }
         }
     );
-});
+});