Spring Cannot enhance @Configuration bean definition

Cannot enhance @Configuration bean definition if its singleton instance has been created too early. Add the corresponding testcase. Fix #22990.

Comment From: snicoll

Thanks for the PR but skipping the enhancement step for circular reference scenarios where the enhanced class won't be used is not going to provide anything. This scenario should be fixed at the user level anyway and we're not keen to add a change for that scenario. Thanks anyway for the PR.