generate-cask-ci-matrix: skip runners the cask is disabled on

[bevanjkay]

• Casks can be disabled on some systems but not others. CI still generated jobs for those systems, where the cask can be neither audited nor installed, so they could only ever fail. filter_runners now drops any runner the cask is disabled on.
• Separately, audit_signing only ever read deprecated?/deprecation_reason. disable! sets those while its date is in the future, but switches to disabled?/disable_reason once it passes. So make the audit resilient to this in case a contributor runs the audit directly locally.

Fixes #23789

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I used claude-code with Opus 5 to generate the fix, and reviewed the logic myself.

[Copilot]

🟢 Approval recommended

The behavioural changes are focused and tested, with only a minor maintainability comment remaining.

Review details

• Files reviewed: 4/4 changed files
• Comments generated: 1
• Review effort level: Balanced

[MikeMcQuaid]

Thanks!