test/dev-cmd/audit: Fix test failure [Linux]

Fix the test failure:
FormulaAuditor#audit_deps a dependency on a macOS-provided keg-only formula
which is not whitelisted problems should match [/unnecessary/]
Failure/Error: its(:problems) { are_expected.to match([/unnecessary/]) }
expected [] to match [/unnecessary/]

Library/Homebrew/test/dev-cmd/audit_spec.rb

@@ -280,7 +280,7 @@ class Foo < Formula
 
         subject { fa }
 
-        its(:problems) { are_expected.to match([/unnecessary/]) }
+        its(:problems, :needs_macos) { are_expected.to match([/unnecessary/]) }
       end
     end
   end