Add a check that RPM can import the same keys as GPG
    
    `rpm --import` seems to be stricter than `gpg --import` on white
    space issues - gpg imported the problematic Fedora 39 key file
    that was just fixed fine, but rpm refused it. So let's check
    that `rpm --import` works on all the keys we check `gpg --import`
    on too.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>