Runner::registerOutOfMemoryShutdownMessage(): write error messages to STDERR

As we may not have access to any of our classes when the process runs out of memory and even if we did, we don't know whether the `StatusWriter` is paused, so to ensure that this out of memory helper info is send to `STDERR`, use a direct call to `fwrite(STDERR, ...)`.

Author: jrfnl

src/Runner.php

@@ -922,7 +922,7 @@ static function () use (
             ) {
                 $errorArray = error_get_last();
                 if (is_array($errorArray) === true && strpos($errorArray['message'], $memoryError) !== false) {
-                    echo $errorMsg;
+                    fwrite(STDERR, $errorMsg);
                 }
             }
         );