Run check-missing on development releases as part of CI
    
    This is...wrong, but it's *usefully* wrong.
    
    comps PRs aren't the only thing that can cause check-missing to
    fail. They're not even the most *common* reason for check-missing
    to fail. It's more likely to be caused by a package being retired
    or a source package changing the binary packages it produces.
    
    However, we cannot currently gate package retirements and/or
    binary package set changes on this script. Doing so would require
    a whole ton more work than just...doing this.
    
    Doing this will cause us to notice problems the next time a comps
    PR is touched. This is a definite improvement on us noticing
    whenever I remember to run the script manually.
    
    It will be somewhat annoying/inconvenient for people submitting
    comps requests, but I think the benefit of problems in comps
    getting noticed and fixed much more rapidly outweighs that.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>