Add missing js-reports-container to EE version of mr_widget_options.vue

This is the EE-port of 5ea377a4

ee/app/assets/javascripts/vue_merge_request_widget/mr_widget_options.vue

@@ -270,6 +270,7 @@ export default {
     <div class="mr-section-container">
       <grouped-test-reports-app
         v-if="mr.testResultsPath"
+        class="js-reports-container"
         :endpoint="mr.testResultsPath"
       />
       <div class="mr-widget-section">