[ci] Reduce windows GPU, windows cpu, and macOS unittest coverage to one version of python

[seemethere]

We should reduce the coverage for windows GPU unittest down to one version of python since running it for all version so python is expensive and probably doesn't provide good signal since the differences between the python version can be caught on a much less expensive configuration (like linux).

cc @peterjc123 @maxluk @nbcsm @guyang3532 @gunandrose4u @smartcat2010 @mszhanyi @pytorch/pytorch-dev-infra

[seemethere]

In the same vein it's also probably not necessary to test multiple versions of python on linux GPU either

[seemethere]

Closed with #2256