Ensure fuchsia artifacts are uploaded correctly

[jtmcdole]

Most engine artifacts are uploaded to gcp buckets; but the linux_fuchsia has a custom step for uploading:

https://github.com/flutter/flutter/blob/master/engine/src/flutter/ci/builders/linux_fuchsia.json

Update these to either have REVISION replaced a second time by the CAH - or add new tasks.

[github-actions]

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