GH-16067: test current output

So that it is clear what changes

Author: DanielEScherzer

Zend/tests/anon/gh16067.phpt

@@ -0,0 +1,11 @@
+--TEST--
+Compiler prevents explicit `abstract` methods on anonymous classes
+--FILE--
+<?php
+
+$c = new class {
+    abstract public function f();
+}
+?>
+--EXPECTF--
+Fatal error: Class class@anonymous must implement 1 abstract method (class@anonymous::f) in %s on line 3