audit: output new formula issue comment failure message.

This should help debug when this fails to be created.

Library/Homebrew/dev-cmd/audit.rb

@@ -143,8 +143,8 @@ module Homebrew
         if GitHub.create_issue_comment(new_formula_problem_lines.join("\n"))
           created_pr_comment = true
         end
-      rescue *GitHub.api_errors
+      rescue *GitHub.api_errors => e
-        nil
+        opoo "Unable to create issue comment: #{e.message}"
       end
     end