formula_auditor: disallow external tap dependencies in core
formula_auditor: disallow external tap dependencies in core

Occasionally, we get PRs that attempt to add a dependency on a formula
in an external tap in homebrew/core (e.g. Homebrew/homebrew-core#94791).

We don't actually have an audit that disallows that. We should have one.

MikeMcQuaid/brew,MikeMcQuaid/brew,JCount/brew,nandub/brew,MikeMcQuaid/brew,Homebrew/brew,Homebrew/brew,nandub/brew,JCount/brew,Homebrew/brew,Homebrew/brew,JCount/brew,MikeMcQuaid/brew,nandub/brew,JCount/brew,nandub/brew