Decrease zend.max_allowed_stack_size in stack_limit_015.phpt

With the stack size of 128K the compile-time stack guard does not fire on 32bit Windows tests, reducing it to 64K

Closes phpGH-21736

Author: shivammathur

Zend/tests/stack_limit/stack_limit_015.phpt

@@ -9,7 +9,7 @@ if (!function_exists('zend_test_zend_call_stack_get')) die("skip zend_test_zend_
 --EXTENSIONS--
 zend_test
 --INI--
-zend.max_allowed_stack_size=128K
+zend.max_allowed_stack_size=64K
 --FILE--
 <?php