Running a 3.8 copr build as well.

Got this on Python 3.8:

=================================== FAILURES ===================================
______________________ TestNbConvertApp.test_allow_errors ______________________

self = <nbconvert.tests.test_nbconvertapp.TestNbConvertApp testMethod=test_allow_errors>

    def test_allow_errors(self):
        """
        Verify that conversion is aborted with '--execute' if an error is
        encountered, but that conversion continues if '--allow-errors' is
        used in addition.
        """
        with self.create_temp_cwd(['notebook3*.ipynb']):
            # Convert notebook containing a cell that raises an error,
            # both without and with cell execution enabled.
            output1, _ = self.nbconvert('--to markdown --stdout notebook3*.ipynb')  # no cell execution
            output2, _ = self.nbconvert('--to markdown --allow-errors --stdout notebook3*.ipynb')  # no cell execution; --allow-errors should have no effect
            output3, _ = self.nbconvert('--execute --allow-errors --to markdown --stdout notebook3*.ipynb')  # with cell execution; errors are allowed

            # Un-executed outputs should not contain either
            # of the two numbers computed in the notebook.
            assert '23' not in output1
            assert '42' not in output1
            assert '23' not in output2
            assert '42' not in output2

            # Executed output should contain both numbers.
            assert '23' in output3
>           assert '42' in output3
E           AssertionError: assert '42' in '\n# Notebook with errors\n\nThis notebook contains a cell which deliberately throws an exception. This is to test if ...n\n```python\nprint("The answer to the question about life, the universe and everything is: {}".format(43 - 1))\n```\n'

nbconvert/tests/test_nbconvertapp.py:382: AssertionError
=============================== warnings summary ===============================

But not in my mock, only in Copr. Maybe the test is flaky. Feel free to merge as is.

Second copr build passed \o/