CI: Avoid passing attrs=None
Trying to fix the allowed-failure build on Travis; I haven't been able to reproduce that error locally, so this is a shot in the dark.
Any chance getting rid of `raise_with_traceback` helps identify? Seems like that is a Python2/3 compat thing so might be making things worse I tend to agree.  Hard to tell until I find a way to reproduce locally Closing in favor of #29174