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This PR enables the codesigning audit for all casks. Currently this audit is only applied to new casks.

The audit is skipped when a cask is deprecated for any reason - so to unblock CI we will need to add a deprecation with reason :unsigned to any casks receiving updates that aren't codesigned.

We need to be aware of some instances of false-positives with the audit, which include when binaries are placed in non-conventional locations within an app bundle. There may be improvements that could be made to the audit for these.

Paging @homebrew/cask as this is a fairly significant change.