Use docker-build env to access GHCR_PAT (#107655)
This will restrict the access to GHCR_PAT to only [docker-build](https://github.com/pytorch/pytorch/settings/environments/1258682414/edit) env.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/107655
Approved by: https://github.com/clee2000, https://github.com/atalman
