Move win-vs2019 build and test to unstable (#100281)
As described in https://github.com/pytorch/pytorch/issues/100273, the vs2019 test jobs are failing due to numpy incompatibility
They've been disabled for a quick response, and now moving them to unstable so that we can keep getting signal on those jobs
Fixes https://github.com/pytorch/pytorch/issues/100273
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100281
Approved by: https://github.com/huydhn
