Update python-validate-pyproject to version 0.13 / rev 4 via SR 1089776
    
    https://build.opensuse.org/request/show/1089776
    by user dgarcia + dimstar_suse
    - Update to 0.13:
      * Make it clear when using input from ``stdin``, #96
      * Fix summary for ``allOf``, #100
      * ``setuptools`` plugin:
        * Improve validation of ``attr`` directives, #101