[skip ci] Ignore snmp test on asan that frequently times out

Not sure why this happens only on master.

Cherry-picked from becf207d0c
No longer happens just on master. ;)

ext/snmp/tests/gh16959.phpt

@@ -5,6 +5,7 @@ snmp
 --SKIPIF--
 <?php
 require_once(__DIR__.'/skipif.inc');
+if (getenv('SKIP_ASAN')) die('skip Causes timeout on asan');
 ?>
 --FILE--
 <?php