I'm not sure why this only happens with py3, but this error code doesn't map to
any of the 3 currently being handled, and kills run-tests.py before it can run
any tests when it happens:
OSError: [WinError 10013] An attempt was made to access a socket in a way forbidden by its access permissions
The documentation[1] says this can happen if another process is bound to the
address with exclusive access. This seems to keep it happy.
[1] https://docs.microsoft.com/en-us/windows/win32/winsock/windows-sockets-error-codes-2