Use shared Windows runners for CI
Now that libffi builds fine when using a Rust MSVC toolchain, we can use GitLab.com's shared Windows runners. This reduces pressure on the MacStadium Mac Mini, allowing it to better focus on macOS tests.
Now that libffi builds fine when using a Rust MSVC toolchain, we can use GitLab.com's shared Windows runners. This reduces pressure on the MacStadium Mac Mini, allowing it to better focus on macOS tests.