Fix gh16811.phpt on CircleCI ARM

CircleCI ARM passes -d zend_test.observer.show_output=0 globally.
The test relied on the default (1) instead of setting it explicitly,
so the <!-- init --> lines were suppressed.

Author: iliaal

ext/zend_test/tests/gh16811.phpt

@@ -4,6 +4,7 @@ GH-16811 (Segmentation fault in zend observer)
 zend_test
 --INI--
 zend_test.observer.enabled=1
+zend_test.observer.show_output=1
 zend_test.observer.observe_function_names=a,d
 --FILE--
 <?php