Use find_spec() in meta importer
The `find_module()` method of meta importers has been deprecated for a
long time. Python 3.12 no longer falls back to `find_module()`.
See: https://docs.python.org/3.12/whatsnew/3.12.html#removed
Related: https://pagure.io/freeipa/issue/9437
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Alexander Bokovoy <abbra@users.noreply.github.com>