fix: Update broken specs (#8651)

- Use fakeTimer for time.spec.js
- Use default sort as last_activity_at_desc
- Update specs for getAllConversations getter

app/javascript/dashboard/store/modules/conversations/helpers.js

@@ -108,6 +108,7 @@ const sortConfig = {
 };
 
 export const sortComparator = (a, b, sortKey) => {
-  const [sortMethod, sortDirection] = SORT_OPTIONS[sortKey] || [];
+  const [sortMethod, sortDirection] =
+    SORT_OPTIONS[sortKey] || SORT_OPTIONS.last_activity_at_desc;
   return sortConfig[sortMethod](a, b, sortDirection);
 };