Fix projects-by-security-status widget for Safari

* Makes sure that the projects by security status widget
  renders correctly in Safari < 14

ee/app/assets/javascripts/security_dashboard/components/first_class_vulnerability_severities.vue

@@ -166,7 +166,7 @@ export default {
           :accordion-id="accordionId"
           :disabled="shouldAccordionItemBeDisabled(severityGroup)"
           :max-height="$options.accordionItemsContentMaxHeight"
-          class="gl-display-flex gl-flex-fill-1 gl-flex-direction-column gl-justify-content-center"
+          class="gl-display-flex gl-flex-grow-1 gl-flex-direction-column gl-justify-content-center"
         >
           <template #title="{ isExpanded, isDisabled }">
             <h5