Update shim for new VERSION location

[thejcannon]

See pantsbuild/pants#17563 for the pants repo change.

[chrisjrn]

Soooo, I think we might actually need to make the PANTS_FROM_SHA functionality a bit smarter, because it’s going to break if you’re testing commits a few months either side of now -- you need the new script for newer versions, and the old script for older versions.

Can we ask GitHub the timestamp of a specific Pants commit and then decide on the URL based on whether it's older or newer than a specific timestamp?

[chrisjrn]

It looks like you can use the GitHub compare commits endpoint without authentication:

% curl \
  -H "Accept: application/vnd.github+json" \
  https://api.github.com/repos/pantsbuild/pants/compare/169d2e613cad7b1bd2593ae9e747100458bf2e5f...66edd8917f5c57b8ab0e36c88dc556142b321732 | grep \"status\"
  "status": "behind",

That status field will give either ahead, behind, or identical. So you can check to see if the requested SHA is behind the changeover commit, and in that case, use the old URL version.

[thejcannon]

Going to drop in favor of a symlink