gating.yaml: duplicate the stanzas
    
    The Gating spec[1] used to recommend having one type of
    YAML stanza for master, one for released branches. We
    just discovered today that this breaks when master
    forks into a release branch: the string 'stable'
    needs to be manually changed to 'testing', and
    nobody is going to remember to do that, and I can't
    think of a (non-tedious) way to add automated checks.
    
    As of 2019-08 (09d7d4f), though, the Gating spec suggests
    having *both* stanzas together in the same gating.yaml
    file. @pingou himself concurs[2]. Although this is
    horrible duplication -- two hundred characters, repeated
    with only six of those different -- it seems cleaner
    than the maintenance burden of having to update
    release branches.
    
     [1] https://docs.fedoraproject.org/en-US/ci/gating/
     [2] https://src.fedoraproject.org/rpms/podman/pull-request/33
    
    Oh, also, add a new 'subject_type' line apparently "required"
    even though things seem to have been working fine without it.
    (Source: same commit, 09d7d4f, on gating.adoc).
    
    Signed-off-by: Ed Santiago <santiago@redhat.com>