[DOC]: fix setFileExtension() xml mapping documentation (#11905)

* doc: fix setFileExtension() xml mapping documentation

* Update docs/en/reference/xml-mapping.rst

Co-authored-by: Grégoire Paris <[email protected]>

---------

Co-authored-by: Grégoire Paris <[email protected]>

Author: rela589n

docs/en/reference/xml-mapping.rst

@@ -46,7 +46,7 @@ In order to work, this requires certain conventions:
 .. code-block:: php
 
     <?php
-    $driver->setFileExtension('.xml');
+    $driver->getLocator()->setFileExtension('.xml');
 
 It is recommended to put all XML mapping documents in a single
 folder but you can spread the documents over several folders if you