Disable modular repos for Rawhide upgrades to avoid #2228827
    
    As 'real' upgrades (using releases/development/rawhide on the
    mirrors) do not hit this bug because it has a stale Modular
    tree, it makes sense to work around the bug in testing so we can
    see if upgrades are broken in any *other* way.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>