[skip ci] Mark another phar test as flaky on macOS

ext/phar/tests/phar_oo_iswriteable.phpt

@@ -5,6 +5,12 @@ phar
 --INI--
 phar.readonly=0
 phar.require_hash=0
+--SKIPIF--
+<?php
+if (getenv("GITHUB_ACTIONS") && PHP_OS_FAMILY === "Darwin") {
+    die("flaky Occasionally segfaults on macOS for unknown reasons");
+}
+?>
 --FILE--
 <?php
 $fname = __DIR__ . '/' . basename(__FILE__, '.php') . '.1.phar.php';