audit: tweak assert/refute_predicate audit
audit: tweak assert/refute_predicate audit

Addresses some of the issues I raised in https://github.com/Homebrew/homebrew-core/pull/19127#issue-263566817.
Would still like to work out a way to check `File.exist?`-style language
inside the `test do` block exclusively but for now it's better to be
too conservative on the audit than to be overly-zealous and flag too
much.

MikeMcQuaid/brew,sjackman/homebrew,konqui/brew,pseudocody/brew,MikeMcQuaid/brew,maxim-belkin/brew,aw1621107/brew,sjackman/homebrew,nandub/brew,ilovezfs/brew,reitermarkus/brew,claui/brew,alyssais/brew,sjackman/homebrew,konqui/brew,JCount/brew,palxex/brew,JCount/brew,MikeMcQuaid/brew,EricFromCanada/brew,nandub/brew,jmsundar/brew,konqui/brew,ilovezfs/brew,DomT4/brew,palxex/brew,mgrimes/brew,EricFromCanada/brew,reelsense/brew,DomT4/brew,DomT4/brew,maxim-belkin/brew,nandub/brew,palxex/brew,mahori/brew,JCount/brew,Linuxbrew/brew,claui/brew,vitorgalvao/brew,sjackman/homebrew,konqui/brew,claui/brew,claui/brew,JCount/brew,hanxue/linuxbrew,mahori/brew,alyssais/brew,reelsense/brew,alyssais/brew,hanxue/linuxbrew,vitorgalvao/brew,Linuxbrew/brew,ilovezfs/brew,mahori/brew,reitermarkus/brew,Homebrew/brew,mgrimes/brew,Linuxbrew/brew,maxim-belkin/brew,Linuxbrew/brew,mgrimes/brew,pseudocody/brew,aw1621107/brew,vitorgalvao/brew,nandub/brew,reelsense/brew,reitermarkus/brew,hanxue/linuxbrew,Homebrew/brew,reitermarkus/brew,DomT4/brew,aw1621107/brew,jmsundar/brew,MikeMcQuaid/brew,pseudocody/brew,Homebrew/brew,Homebrew/brew,vitorgalvao/brew,mahori/brew,EricFromCanada/brew,EricFromCanada/brew,jmsundar/brew