This is not urgent because this happens only when webkit_python_test (with patch) failed by the CL.

The error message is:
typ: error: unrecognized arguments: --test-list=/b/s/w/it6Yk_HK/tmpWCpFno

It seems that we are passing --test-list to run_blinkpy_tests.py which doesn't expect --test-list.

https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8931766766988561664/+/steps/webkit_python_tests__without_patch_/0/stdout