[ci][ez] Rename artifact from process_artifacts_combined

Build artifacts are uniquely associated to a single workflow run, so
appending the sha was unnecessary. I originally included it to make it
easier to download later but this turns out to be unneeded.

Drops the sha suffix to make downloading the artifact in a separate
script / workflow more straightforward.

ghstack-source-id: 36ac4df4c35409fd08fbfa8714043eb556ff88d3
Pull Request resolved: facebook#30364