Fix: Render field_block_item from block_content entity in accordion template

Fixed the rendering of the field_block_item field in the accordion block template (lb_accordion). Previously, the template was using content.field_block_item, which is not always available depending on the view mode configuration. This caused the accordion items to not render properly. The fix switches to using block_content.field_block_item directly, which ensures reliable access to the referenced entities regardless of view mode settings.