formula_auditor: skip non-core compatibility bumps check

[scpeters]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew lgtm (style, typechecking and tests) with your changes locally?

---

The audit added in #20936 doesn't always make sense for formulae in 3rd-party taps, which may need to be revision bumped in order to rebuild bottles after a core formula changes. When minor or major upgrades are made in homebrew-core, we typically recursively remove bottles of dependents in our 3rd-party tap; for example see the tracking issue osrf/homebrew-simulation#3270 and dependent bottle removal PR osrf/homebrew-simulation#3271 opened in response to the libwebsockets update to 4.5.0 in Homebrew/homebrew-core#256449. After quickly removing the broken bottles, we open a separate pull request with revision bumps in order to rebuild bottles, such as osrf/homebrew-simulation#3272, which currently fails the compatibility bumps check.

I read the feature request for compatibility_version in #19202, but I'm not sure why it should be added to a pull request like osrf/homebrew-simulation#3272. I opened this PR to disable the check for non-core formulae, which would resolve my issue, but I am open to other suggestions.

[MikeMcQuaid]

I'm not sure this is the right thing.

The intention of compatibility_version is that we can rely on that rather than versions/revisions to detect whether we need to upgrade a dependency. We used to assume "we need the newest version of every recursive dependency always". We then went "we need at least the version declared in the bottle manifest". Compatability version allows us to say "we need at least this compatibility version" which means we can avoid upgrading dependencies unnecessarily when their ABI or API doesn't change.

This check should instead do something like check if things are bottled. It doesn't make sense when building from source but does make sense if you're installing bottles.