[openstacksdk][older pythons] Reverting a small mypy change in openstackapi

Hi,

I discovered the issue fixed by https://review.opendev.org/c/openstack/openstacksdk/+/915199 accidentally while rebased Kerbside patches, and I am wondering who I should ask nicely for a review. Its a relatively small change, but does regress mypy support in return for working correctly on python versions below python 3.10, which we promise to support right now.

Thanks, Michael