AutoBuilder is not honoring the osType field of the subscription

Recently, there have been out-of-band updates to Windows images. This has caused AutoBuilder to run the pipeline to rebuild Windows images in the dotnet-docker repo. This shouldn't be happening according to the settings of the subscription for that repo which should be filtering it to only Linux images ([example](https://github.com/dotnet/docker-tools/blob/314c0ca6b6eb5f49aafbf5dcf6ba58225f355277/eng/check-base-image-subscriptions.json#L59)).