Disable SHA256 header-only digest generation temporarily (#1480407)
    
    There's a bug in rpm 4.13.x rpmkeys -K signature checking that chokes
    on unknown tags it's supposed to ignore like older rpm versions do.
    Unfortunately that means all active Fedora versions are affected,
    so disabling the SHA256 header-only digest generation temporarily to
    give time to deal with the other versions.