ci: avoid pounding on the poor ci-artifacts container

ci: avoid pounding on the poor ci-artifacts container

When this developer tested how the git-sdk-64-minimal artifact could be
served to all the GitHub workflow runs that need it, Azure Blobs looked
like a pretty good choice: it is reliable, fast and we already use it in
Git for Windows to serve components like OpenSSL, cURL, etc

It came as an unpleasant surprise just _how many_ times this artifact
was downloaded. It exploded the bandwidth to a point where the free tier
would no longer be enough, threatening to block other, essential Git for
Windows services.

Let's switch back to using the Build Artifacts of our trusty Azure
Pipeline for the time being.

To avoid unnecessary hammering of the Azure Pipeline artifacts, we use
the GitHub Action `actions/upload-artifact` in the `windows-build` job
and the GitHub Action `actions/download-artifact` in the `windows-test`
and `vs-test` jobs (the latter now depends on `windows-build` for that
reason, too).

Helped-by: Đoàn Trần Công Danh <congdanhqx@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>