Call `#feature_available?` with `current_user`

In EE, the second parameter `user` is made optional.
However, in the core code,
`user` is still required.

app/views/shared/issuable/_bulk_update_sidebar.html.haml

 - type = local_assigns.fetch(:type)
 - bulk_issue_health_status_flag = type == :issues && @project&.group&.feature_available?(:issuable_health_status)
 - epic_bulk_edit_flag = @project&.group&.feature_available?(:epics) && type == :issues
-- bulk_iterations_flag = @project.feature_available?(:iterations) && @project&.group.present? && type == :issues
+- bulk_iterations_flag = @project.feature_available?(:iterations, current_user) && @project&.group.present? && type == :issues
 
 %aside.issues-bulk-update.js-right-sidebar.right-sidebar{ "aria-live" => "polite", data: { 'signed-in': current_user.present? } }
   .issuable-sidebar.hidden