packaging: add pygit2 to the py3 Windows installers
This is needed to be able to use the git extension.
The extension no longer complains about the library being not installed, but
hg log -r . on a repo that works in WSL yielded a TypeError:
... File "mercurial.hg", line 188, in _peerorrepo File "mercurial.localrepo", line 3224, in instance File "mercurial.localrepo", line 623, in makelocalrepository File "hgext.git", line 117, in _makestore File "hgext.git", line 48, in __init__ TypeError: Repository unable to unpack backend.
Differential Revision: https://phab.mercurial-scm.org/D9405