fedora.conf: add mesa-vulkan-drivers into multilib_whitelist
    
    Vulkan drivers need to be accessible for i686 as well. Currently it's missing
    for updates-testing builds, which is causing issues for our users, see:
    https://bodhi.fedoraproject.org/updates/FEDORA-2022-4120f31977#comment-2466325
    https://bodhi.fedoraproject.org/updates/FEDORA-2022-db6aea82e4
    
    Signed-off-by: Kamil Páral <kparal@redhat.com>