Tests: Remove use of xml_set_object() in TestXMLParser.

The XML Parser extension still supports a quite dated mechanism for method based callbacks, where the object is first set via `xml_set_object()` and the callbacks are then set by passing only the name of the method to the relevant parameters on any of the `xml_set_*_handler()` functions.

{{{
xml_set_object( $parser, $my_obj );
xml_set_character_data_handler( $parser, 'method_name_on_my_obj' );
}}}

Passing proper callables to the `xml_set_*_handler()` functions has been supported for the longest time and is cross-version compatible. So the above code is 100% equivalent to:

{{{
xml_set_character_data_handler( $parser, [$my_obj, 'method_name_on_my_obj'] );
}}}

The mechanism of setting the callbacks with `xml_set_object()` has now been deprecated as of PHP 8.4, in favour of passing proper callables to the `xml_set_*_handler()` functions. This is also means that calling the `xml_set_object()` function is deprecated as well.

This commit fixes this deprecation for the `TestXMLParser` helper utility. In this case, the callbacks were already using the recommended format and the call to `xml_set_object()` was completely redundant.

As this is a test utility and was already causing pre-existing tests using the utility to fail, there is no need for dedicated tests to cover this change.

Refs:
* https://wiki.php.net/rfc/deprecations_php_8_4#xml_set_object_and_xml_set_handler_with_string_method_names
* https://www.php.net/manual/en/function.xml-set-object.php
* https://www.php.net/manual/en/ref.xml.php

Follow-up to [25002].

Props jrf.
See #62061.
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git-svn-id: http://core.svn.wordpress.org/trunk@58451 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.7-alpha-59054';
+$wp_version = '6.7-alpha-59055';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.