Update PHPUnit configuration

Author: sebastianbergmann

phpunit.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/12.2/phpunit.xsd"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/12.3/phpunit.xsd"
          bootstrap="vendor/autoload.php"
          cacheDirectory=".phpunit.cache"
          executionOrder="depends,defects"