[ci]: Use macOS arm runner for intel builds (#93330)
The intel runners were quite a bit slower than the base arm runners. We
were previously compiling both architectures on self-hosted arm so this
just back the status quo on GH runners to improve speed. This shaves off
~10/20 mins.
Validated
[here](https://github.com/vercel/next.js/actions/runs/25071926790/job/73454315459)
