Restore the lost success event handler for hiding the verification modal

Changelog: fixed
EE: true

ee/app/assets/javascripts/billings/components/account_verification_modal.vue

@@ -70,6 +70,7 @@ export default {
       :initial-height="$options.iframeHeight"
       :iframe-url="iframeUrl"
       :allowed-origin="allowedOrigin"
+      @success="$emit('success')"
     />
   </gl-modal>
 </template>

ee/spec/frontend/billings/components/account_verification_modal_spec.js

 import { GlSprintf } from '@gitlab/ui';
 import { shallowMount } from '@vue/test-utils';
 import AccountVerificationModal from 'ee/billings/components/account_verification_modal.vue';
+import Zuora from 'ee/billings/components/zuora.vue';
 
 describe('Account verification modal', () => {
   let wrapper;
@@ -39,6 +40,18 @@ describe('Account verification modal', () => {
     });
   });
 
+  describe('when zuora emits success', () => {
+    beforeEach(() => {
+      createComponent();
+    });
+
+    it('forwards the success event up', () => {
+      wrapper.findComponent(Zuora).vm.$emit('success');
+
+      expect(wrapper.emitted('success')).toHaveLength(1);
+    });
+  });
+
   describe('clicking the submit button', () => {
     beforeEach(() => {
       createComponent();