Update bug72479.phpt UAF test

bug72479.phpt tested a UAF via unserialize() of SNMP. With
NOT_SERIALIZABLE, unserialize() rejects the class entirely, preventing
the UAF by construction. Update the test to verify the rejection.

Author: iliaal

ext/snmp/tests/bug72479.phpt

@@ -10,28 +10,12 @@ require_once(__DIR__.'/skipif.inc');
 <?php
 $arr = [1, [1, 2, 3, 4, 5], 3, 4, 5];
 $poc = 'a:3:{i:1;N;i:2;O:4:"snmp":1:{s:11:"quick_print";'.serialize($arr).'}i:1;R:7;}';
-$out = unserialize($poc);
-gc_collect_cycles();
-$fakezval = ptr2str(1122334455);
-$fakezval .= ptr2str(0);
-$fakezval .= "\x00\x00\x00\x00";
-$fakezval .= "\x01";
-$fakezval .= "\x00";
-$fakezval .= "\x00\x00";
-for ($i = 0; $i < 5; $i++) {
-    $v[$i] = $fakezval.$i;
-}
-var_dump($out[1]);
-
-function ptr2str($ptr)
-{
-    $out = '';
-    for ($i = 0; $i < 8; $i++) {
-        $out .= chr($ptr & 0xff);
-        $ptr >>= 8;
-    }
-    return $out;
+try {
+    $out = unserialize($poc);
+    var_dump($out);
+} catch (Exception $e) {
+    echo $e->getMessage() . "\n";
 }
 ?>
 --EXPECT--
-int(1)
+Unserialization of 'SNMP' is not allowed