NamingConventions/PrefixAllGlobals: modify a test to use readonly anonymous classes

This commit modifies an existing test to use readonly anonymous classes to the `WordPress.NamingConventions.PrefixAllGlobals` tests. This is just to ensure that the part of the sniff code that checks for `T_ANON_CLASS` tokens works correctly with readonly anonymous class added in PHP 8.3.

The sniff was already handling readonly anonymous classes correctly, and no change to the sniff code is needed.

Author: rodrigoprimo

WordPress/Tests/NamingConventions/PrefixAllGlobalsUnitTest.1.inc

@@ -137,7 +137,7 @@ class Acronym_Example {
 	function do_something( $param = 'default' ) {}
 }
 
-$acronym_class = new class {
+$acronym_class = new readonly class {
 	const SOME_CONSTANT = 'value';
 
 	public $var = 'abc';