fix: replace unknown method loadFromExtension with extension

Author: vinceAmstoutz

reference/configuration/debug.rst

@@ -95,7 +95,7 @@ Typically, you would set this to ``php://stderr``:
     .. code-block:: php
 
         // config/packages/debug.php
-        $container->loadFromExtension('debug', [
+        $container->extension('debug', [
             'dump_destination' => 'php://stderr',
         ]);