Recent Windows CI issues

Hi GHC devs, Me and Magnus have brought up a new temporary windows runner to address the recent GHC CI traffic jam, as a part of our joint work to make CI faster. If you see your windows CI job fails with T17912, before retrying the job, please rebase your branch against the latest master branch, so that it includes latest fixes and can reliably pass on the new runner. If you spot other spurious windows CI failures, please open a new issue and tag us. Cheers, Cheng Shao