Formatted descriptions are not displayed

Element's description not being displayed if it is a formatted text and represented as a render element.

includes/webform.theme.inc

$variables['description']['content'] = [
        '#type' => 'container',
        '#attributes' => new Attribute($description_attributes),
      ] + $description;

So a container element type is used. And description array is being concatenated with it instead of being inserted as a child. It works when description is a ['#markup' => $element['#description'] array but not when it's a separate render element like this:

Array
(
    [#type] => processed_text
    [#text] => Voornaam
    [#format] => full_html
)

Description array should be inserted as a child of the container array.