Make phpdbg test portable

Author: cmb69

sapi/phpdbg/tests/phpdbg_get_executable_stream_wrapper.phpt

@@ -70,7 +70,7 @@ stream_wrapper_register('wrapper', StreamWrapper::class);
  * Next, we include a PHP file that contains executable lines, via the stream
  * wrapper.
  */
-$filename = __DIR__ . '/phpdbg_get_executable_stream_wrapper.inc';
+$filename = __DIR__ . DIRECTORY_SEPARATOR . 'phpdbg_get_executable_stream_wrapper.inc';
 require 'wrapper://' . $filename;
 
 /**