[CI] try PHP 8.1 bump

Author: TomasVotruba

rector.php

@@ -18,7 +18,7 @@
 
 return static function (ContainerConfigurator $containerConfigurator): void {
     // include the latest PHP version + all bellow in one config!
-    $containerConfigurator->import(LevelSetList::UP_TO_PHP_80);
+    $containerConfigurator->import(LevelSetList::UP_TO_PHP_81);
 
     // include sets
     $containerConfigurator->import(SetList::CODING_STYLE);