Dynamic property deprecation warnings in PHP 8.2

[mikemanger]

This is fixable by adding the #[\AllowDynamicProperties] class attribute.

[wp-content/plugins/multiple-post-thumbnails/multi-post-thumbnails.php:79] Creation of dynamic property MultiPostThumbnails::$label is deprecated
[wp-content/plugins/multiple-post-thumbnails/multi-post-thumbnails.php:79] Creation of dynamic property MultiPostThumbnails::$id is deprecated
[wp-content/plugins/multiple-post-thumbnails/multi-post-thumbnails.php:79] Creation of dynamic property MultiPostThumbnails::$post_type is deprecated
[wp-content/plugins/multiple-post-thumbnails/multi-post-thumbnails.php:79] Creation of dynamic property MultiPostThumbnails::$priority is deprecated
[wp-content/plugins/multiple-post-thumbnails/multi-post-thumbnails.php:79] Creation of dynamic property MultiPostThumbnails::$context is deprecated