Use getenv to prevent undefined key warning

Author: nielsdos

sapi/phpdbg/tests/gh12962.phpt

@@ -7,7 +7,7 @@ if (!getenv('TEST_PHPDBG_EXECUTABLE')) die("SKIP: No TEST_PHPDBG_EXECUTABLE spec
 --FILE--
 <?php
 putenv('PHP_INI_SCAN_DIR='.__DIR__."/gh12962");
-passthru($_ENV['TEST_PHPDBG_EXECUTABLE'] . " -q");
+passthru(getenv('TEST_PHPDBG_EXECUTABLE') . " -q");
 ?>
 --EXPECT--
 Executed .phpdbginit