Properly handle MySQL error code 4031 from PHP 8.4

It has been introduced in:
mysql/mysql-server@14508bb

And PHP 8.4 will support it:
php/php-src#13618

src/Driver/API/MySQL/ExceptionConverter.php

@@ -101,6 +101,7 @@ public function convert(Exception $exception, ?Query $query): DriverException
                 return new ConnectionException($exception, $query);
 
             case 2006:
+            case 4031:
                 return new ConnectionLost($exception, $query);
 
             case 1048: