windows-ci: run Windows CI automatically alongside the others
This will enable us to make Windows Python 3 a first-class citizen for the next
6.0 cycle. We will probably get some flaky tests and we're missing others that
are skipped, but we'll turn them on it future patches.
Differential Revision: https://phab.mercurial-scm.org/D11256
local test passed
addgroupcopy test passed
clone test passed
lowlevelcopy test passed
slicing test passed
issnapshot test passed
findsnapshot test passed