Tests fail with Click 8.2 due to removed mix_stderr argument #544

tests/test_krr.py and tests/test_runner.py create CliRunner(mix_stderr=False).

Click 8.2 removed the mix_stderr parameter, so pytest fails during collection with:

TypeError: CliRunner.__init__() got an unexpected keyword argument 'mix_stderr'

Replacing those calls with CliRunner() restores test collection with current Click.