set update_at on bookmarks return when changing sort order (#28807)

* set update_at on bookmarks return when changing sort order

* update bookmarks sort order test

server/channels/store/sqlstore/channel_bookmark_store.go

@@ -270,6 +270,7 @@ func (s *SqlChannelBookmarkStore) UpdateSortOrder(bookmarkId, channelId string,
 	ids := []string{}
 	for index, b := range bookmarks {
 		b.SortOrder = int64(index)
+		b.UpdateAt = now
 		caseStmt = caseStmt.When(sq.Eq{"Id": b.Id}, strconv.FormatInt(int64(index), 10))
 		ids = append(ids, b.Id)
 	}