bots are no longer testing core/std on windows

[brson]

check-fast no longer tests core and std and there are broken tests. oops

[catamorphism]

Nominating for milestone 4, well-covered

[graydon]

accepted for well-covered milestone

[emberian]

Is this still relevant?

/cc @crnobog, who was working on Windows tests

[pnkfelix]

Part of #8844.

[pnkfelix]

Note also PR #5325, where brson attempted to fix this and ran into a deadlock.