Fix Windows tests

[iangmaia]

As reported in #195, Windows unit tests started failing, presumably after all the changes in our Windows AMI.
This PR should fix the Windows unit tests.

[AliSoftware]

Overall my suggestion for the fix is to just completely delete the prepare_windows_host_for_app_distribution.ps1 and its test from the repo.

Once we'll find the time to update all the repos that were still calling prepare_windows_host_for_app_distribution.ps1 in their .buildkite/commands/*.sh scripts and relied on the assumption that they might still be running on the base AMI and not our custom one, we'll have those repos just call setup_windows_code_signing.ps1 directly instead and bump their release-toolkit version to 6.0.0, at which point no repo using release-tookit >5.7.0 will call prepare_windows_host_for_app_distribution.ps1 and it won't be needed anymore (which was the whole point of creating our custom AMI in the first place after all.

[AliSoftware]

Also feel free to make this PR target trunk instead so that it doesn't depend on mine.

Once we merge this PR I can rebase my git-crypt PR onto the new trunk as I continue working on it (as I want to test it on all our agents before I merge it, so it might take some time until it lands)