audit: limit non-failure cask output

[Rylan12]

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This PR changes how brew audit outputs cask audit summaries.

By default, brew audit will not output any passed messaging unless --verbose is passed or there was only one named argument. Warnings will still be shown.

If the --display-failures-only flag is passed, warnings will also be silenced.

I added the --display-failures-only flag to the brew audit calls in the tests workflow. I don't think there's a benefit to seeing the huge number of warnings in this situation. Warnings don't block CI here, so there's no point in showing them as it makes it harder to read when there are failures.

[BrewTestBot]

Review period will end on 2021-03-23 at 00:00:00 UTC.

[reitermarkus]

This is the default for formulae.

Is this because there are no warnings for formulae or are warnings actually hidden by default for formulae?

[Rylan12]

There are no warnings

[Rylan12]

But there's also no message shown if the audit succeeds. It's either no output or a list of problems.

[MikeMcQuaid]

👍🏻 this is a big improvement. I agree with specifically not outputting warnings for Casks in the way we're using it for CI.

[BrewTestBot]

Review period ended.