Update python-xmldiff to version 2.6.3 / rev 22 via SR 1154951
    
    https://build.opensuse.org/request/show/1154951
    by user StevenK + anag+factory
    - Update to 2.6.3:
      * Solved an error in the xmlformatter when using default namespaces. #89
      * #108: Fixed an error that happens if using namespaces like ns0 or ns1.
      * Added `InsertNamespace` and `DeleteNamespace` actions for better handling
        of changing namespaces. Should improve any "Unknown namespace prefix"
        errors. Changing the URI of a a namespace prefix is not supported, and
        will raise an error.
      * Used geometric mean for the node_ratio, for better handling of simple nodes.
      * Added an experimental --best-match method that is slower, but generate
        smaller diffs when you have many nodes that are similar.
      * The -F argument now also affects the --fast-match stage.
      * Make it possible to adjust the attributes considered when comparing nodes.
      * Python versions 3.7