Add test for issue nikic#78

This has been fixed upstream.

Author: nikic

tests/multiple_final_modifiers.phpt

@@ -0,0 +1,21 @@
+--TEST--
+Multiple final multipliers should generate CompileError, not a fatal error
+--SKIPIF--
+<?php if (PHP_VERSION_ID < 70300) die('skip Requires PHP 7.3+'); ?>
+--FILE--
+<?php
+
+$code = <<<'PHP'
+<?php class C {
+    final final function foo($fff) {}
+}
+PHP;
+
+try {
+    ast\parse_code($code, $version=50);
+} catch (CompileError $e) {
+    echo $e->getMessage(), "\n";
+}
+?>
+--EXPECT--
+Multiple final modifiers are not allowed