cask/audit: iterate over artifacts in rosetta/signing audit

[bevanjkay]

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For both audit_rosetta and audit_signing we can run into an inconsistency when two artifacts are present with differing results. This results in there being no way for the cask to pass brew audit at present.

This PR introduces a change that checks all artifacts in the appropriate situation before returning with an error.

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Example: Homebrew/homebrew-cask#223456