Associate manifest.json artifacts for phased JobSteps with original.
Associate manifest.json artifacts for phased JobSteps with original.

Summary:
Manifest files are intended to be associated with the top-level
JobStep. Typically, phased result builds associate artifacts
with the final jobstep, which makes it look like an error.

Fixes T59126

Test Plan: None yet

Reviewers: nate

Reviewed By: nate

Subscribers: changesbot, mkedia

Maniphest Tasks: T59126

Differential Revision: https://tails.corp.dropbox.com/D138819

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