audit: fix non-core versioned formulae handling/

Fixes issue mentioned in #9016.

Library/Homebrew/dev-cmd/audit.rb

@@ -281,7 +281,7 @@ module Homebrew
           problem "#{formula} is versioned but no #{unversioned_name} formula exists"
         end
       elsif @build_stable && formula.stable? &&
-            !(versioned_formulae = formula.versioned_formulae).empty?
+            (versioned_formulae = formula.versioned_formulae - [formula]).present?
         versioned_aliases = formula.aliases.grep(/.@\d/)
         _, last_alias_version = versioned_formulae.map(&:name).last.split("@")
         alias_name_major = "#{formula.name}@#{formula.version.major}"