cask/audit: adjust signing failure error message

[p-linnane]

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"macOS on ARM requires software to be signed." is misleading for the checks we're running. This PR adjusts the messaging for signing failures to better distinguish between Homebrew/cask and third-party taps. url.location also doesn't provide anything meaningful for this audit, so I've removed that to reduce noise.

Before:

 - Signature verification failed:
Progress: 356/356
Scan completed, but failed because the software is not signed by a distributor that meets the system Gatekeeper requirements.

macOS on ARM requires software to be signed.
Please contact the upstream developer to let them know they should sign and notarize their software.
foo
  * line 5, col 2: Signature verification failed:
Progress: 356/356
    Scan completed, but failed because the software is not signed by a distributor that meets the system Gatekeeper requirements.

    macOS on ARM requires software to be signed.
    Please contact the upstream developer to let them know they should sign and notarize their software.
Error: 1 problem in 1 cask detected.

After:

 - Signature verification failed:
Progress: 356/356
Scan completed, but failed because the software is not signed by a distributor that meets the system Gatekeeper requirements.

Homebrew/cask requires all casks to be signed and notarized by Apple.
Please contact the upstream developer and ask them to sign and notarize their software.
foo
  * Signature verification failed:
Progress: 356/356
    Scan completed, but failed because the software is not signed by a distributor that meets the system Gatekeeper requirements.

    Homebrew/cask requires all casks to be signed and notarized by Apple.
    Please contact the upstream developer and ask them to sign and notarize their software.
Error: 1 problem in 1 cask detected.

[Copilot]

Pull Request Overview

This PR updates the error message shown when cask signature verification fails. The changes make the error message more specific to official Homebrew taps by conditionally appending additional guidance.

• Refactored the signing failure error message to be built conditionally
• Added tap-specific guidance for official Homebrew taps about signing requirements

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[Copilot]

Pull Request Overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 1 comment.

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