PHP 8.1 compatibility - set return types on iterator methods
Under PHP 8.1 we receive deprecation notices like this:
Return type of Civi\FormProcessor\Config\SpecificationBag::getIterator() should either be compatible with IteratorAggregate::getIterator(): Traversable, or the #[\ReturnTypeWillChange] attribute should be used to temporarily
suppress the notice in /home/jon/local/mysite/web/sites/all/civicrm/extensions/form_processor/Civi/FormProcessor/Config/SpecificationBag.php on line 99
This fixes those.