decode_args(): make a copy of the opts dict, rather than modifying it in-place
    
    Fixes: #1007
    https://pagure.io/koji/issue/1007
    
      Author: Mike Bonnet <mikeb@redhat.com>
      Date:   Wed Jul 18 17:03:56 2018 -0700
    
        The commit changes make_task() to call decode_args() on the arglist before
        it is saved to the db. If the method was called with keyword arguments, those
        would be passed in a dict at the end of the arglist, with a __starstar entry.
        decode_args() edits that dict in place, removing the __starstar entry and
        making the arglist appear to end in a single dict argument, effectively
        removing the keyword arguments. This change makes a copy of the dict before