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
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).