TASK: Add missing type declaration from Flow 8.3

While branching 8.4, this type declaration got lost and should be added again.

Neos.FluidAdaptor/Classes/ViewHelpers/Form/SelectViewHelper.php

@@ -375,7 +375,7 @@ protected function renderOptionTag(mixed $value, string $label)
             $output .= ' selected="selected"';
         }
 
-        $output .= '>' . htmlspecialchars($label) . '</option>';
+        $output .= '>' . htmlspecialchars((string)$label) . '</option>';
 
         return $output;
     }