Incorrect usage of #markup and the Link object

A recent deprecation fix introduced in #2859215 causes an issue, as the Link object is passed to the form builders #markup element, triggering the following error:

The website encountered an unexpected error. Please try again later.
Recoverable fatal error: Object of class Drupal\Core\Link could not be converted to string in Drupal\Component\Utility\Xss::filter() (line 67 of core/lib/Drupal/Component/Utility/Xss.php).

Instead of using #markup and Link I think we should be using the link element type (https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Render%21...)

$build['examples_link'] = [
  '#title' => $this->t('Examples'),
  '#type' => 'link',
  '#url' => Url::fromRoute('examples.description')
];