contrib: stop installing Python 3.5 and 3.6 in Windows environment
We're only publishing Python 3.7+ wheels and other builds on Windows.
Python 3.5 and 3.6 are not supported on this platform. Let's stop
installing them in the development environment.
Differential Revision: https://phab.mercurial-scm.org/D9185
Martin von Zweigbergk <martinvonz@google.com> [Fri, 09 Oct 2020 09:17:47 -0700] rev 45688
py3: convert an exception message to bytes
One of our users ran into this (unrelated to my recent work on
more specific errors).
Differential Revision: https://phab.mercurial-scm.org/D9184