ci: Use Windows ARM builders

ci: Use Windows ARM builders

Now that native ARM builders are available for windows, we can use
them instead of cross-compiling. This improves parallelism in our build
and speeds things up a bit, plus we can test the windows-arm builds now.

Also stop producing x86_64 builds for macos, since they are redundant
with the universal2 builds (the x86_64 builds were useful with older
version of pip, but they've been fully supported for 5 years now).