entity-meta__title class is a string not an array

In commerce/modules/order/src/Form/OrderForm.php

$form['meta'] = [
      '#attributes' => ['class' => ['entity-meta__header']],
      '#type' => 'container',
      '#group' => 'advanced',
      '#weight' => -100,
      'state' => [
        '#type' => 'html_tag',
        '#tag' => 'h3',
        '#value' => $order->getState()->getLabel(),
        '#attributes' => [
          'class' => 'entity-meta__title',
        ],
        // Hide the rendered state if there's a widget for it.
        '#access' => empty($form['store_id']),
      ],
      'date' => NULL,
      'changed' => $this->fieldAsReadOnly($this->t('Last saved'), $last_saved),
    ];

#attributes' => [
          'class' => 'entity-meta__title',
],

should be

#attributes' => [
          'class' => ['entity-meta__title'],
],

Otherwise it throws errors down the line about not being an array.