[BUGFIX] Ensure, that the ID to add/remove from the list is an integer

Fluid will take care of type casting if the ViewHelper is called non-statically, but does not convert any argument if it is called statically

Classes/ViewHelpers/MultiCategoryLink/ArgumentsViewHelper.php

@@ -69,7 +69,7 @@ public static function renderStatic(
         }
 
         $allArguments = (array)$arguments['additionalParams'];
-        $categoryId = $arguments['item'];
+        $categoryId = (int)$arguments['item'];
 
         $categoryList = $arguments['list'];
         if ($arguments['mode'] === 'add') {