Add "upgrade on edit"
Currently, when a user has created content using a content library, then installs a later version of that library and then edits and saves the existing content, the content will be upgraded to the later library version automatically on other H5P integrations (e.g. the H5P plugins for Drupal 7 or WordPress).
When merged in, the Drupal 9 plugin will do the same instead of merely sending out an error message that the content could not be saved ("Something unexpected happened. We were unable to save this content.") - even though the reason is well known :-) (https://git.drupalcode.org/project/h5p/-/blob/9.x-1.x-dev/modules/h5peditor/src/Plugin/Field/FieldWidget/H5PEditorWidget.php#L93-96)