allow 2 uncleared connections at most

allow 2 uncleared connections at most

tests show that if the code is really broken, we have
5 or more connections lingering here, so for less than two
(it's usually one) just clean it out and consider it as GC noise.

To test this better we also open up the windows/mac archs that
were disabled for greenlet

Fixes: #13102
Change-Id: Iccf419e7f345bcae4a388d222ab69fc792a3c1ca
(cherry picked from commit ff2c7668fe90b43b75dcb0d6e7651349dd715e5a)