Change the copy to use `ActionsArtifact.StoragePath` instead of the
`ArtifactPath`. Skip artifacts that are expired, and don't error if the
file to copy does not exist.
---
When trying to migrate actions artifact storage from local to MinIO, we
encountered errors that prevented the process from completing
successfully:
* The migration tries to copy the files using the per-run
`ArtifactPath`, instead of the unique `StoragePath`.
* Artifacts that have been marked expired and had their files deleted
would throw an error
* Artifacts that are pending, but don't have a file uploaded yet will
throw an error.
This PR addresses these cases, and allow the process to complete
successfully.
(cherry picked from commit 8de8972baf5d82ff7b58ed77d78e8e1869e64eb5)
