Allow to use newer GPG keys, so Rawhide can be updated after branch.
Currently, the GPG keys have to be updated together with repositories.
But there is no strong relationship between them. After branching, there
has has to be possible to update GPG keys independently, otherwise, it
is not possible to keep updating Rawhide without usign --nogpgcheck or
different "cheating".
Original discussion of fedora-devel:
https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/thread/MFX2JDVANNEW7LWWIBBLYCN6DEPWHSXF/
Signed-off-by: Vít Ondruch <vondruch@redhat.com>