Prior to 2.9 the the backup mimetype could use zip packer for opening the backup file. In 2.9 the mimetype ('application/vnd.moodle.backup') requires mbz packer. The adjustment applies a more generic approach in mod_dataform_preset_manager::apply_preset() by getting a file packer for the backup mimetype rather than the current hardcoded zip packer. This should be backwards compatible with 2.8.