Summary:
The breakage has been fixed, so bring back the manifest, but only the Linux one, because the Mac version is failing due to another issue.

Also to make it easier to debug issues on GitHub Actions separate out the dependencies build from Mononoke and rust-shed builds.

Reviewed By: krallin

Differential Revision: D21448412

fbshipit-source-id: 68d89c858d1692727a7fd66bca114920e6dfb4dc