https://fusion.corp.google.com/projectanalysis/summary/KOKORO/prod%3Agrpc%2Fcore%2Fmaster%2Flinux%2Fgrpc_basictests_python

https://source.cloud.google.com/results/invocations/baba7e4f-6421-4b0c-8cb7-b106b252191d/log

https://fusion.corp.google.com/projectanalysis/summary/KOKORO/prod%3Agrpc%2Fcore%2Fmaster%2Fwindows%2Fgrpc_basictests_python

https://source.cloud.google.com/results/invocations/9cd6212f-643a-4c47-9ef6-76b482a60932/targets/github%2Fgrpc%2Ftoplevel_run_tests_invocations%2Frun_tests_python_windows_opt_native/tests

It started failing yesterday, when setuptools releases 50.0.0. It's highly likely that their latest build broke us.

CC @jtattermusch @gnossen