[Caffe2] Increase timing threshold to 50 ms on Windows (#37892)
Summary:
Helps prevent following accidental failures:
```
..\caffe2\core\parallel_net_test.cc:303
The difference between ms and 350 is 41, which exceeds kTimeThreshold, where
ms evaluates to 391,
350 evaluates to 350, and
kTimeThreshold evaluates to 40.
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37892
Differential Revision: D21417251
Pulled By: malfet
fbshipit-source-id: 300cff7042e466f014850cc7cc406c725d5d0c04
