[ci] Fork scripts/release/download-experimental-build.js

This PR just copies the original file without any modifications for
easier review.

The original script makes assumptions about CircleCI that are difficult
to untangle. So let's fork this file temporarily for GitHub actions.
Later on we will remove the original and rename this fork back to the
original naming.

ghstack-source-id: 0ce0785
Pull Request resolved: facebook#30374

Author: felixshiftellecon