Issue #3436741 make Automatic Updates Extension stable

Closes #3436741

automatic_updates_extensions/src/Form/UpdateReady.php

@@ -133,7 +133,11 @@ final class UpdateReady extends UpdateFormBase {
     $form['package_updates'] = $this->showUpdates();
     $form['backup'] = [
       '#prefix' => '<strong>',
-      '#markup' => $this->t('Back up your database and site before you continue. <a href=":backup_url">Learn how</a>.', [':backup_url' => 'https://www.drupal.org/node/22281']),
+      '#type' => 'checkbox',
+      '#title' => $this->t('Warning: Updating contribute projects may leave your site inoperable.'),
+      '#description' => $this->t('Back up your database and site before you continue. <a href=":backup_url">Learn how</a>. If possible, it is highly recommended that you test this update in a development environment first.', [':backup_url' => 'https://www.drupal.org/node/22281']),
+      '#required' => TRUE,
+      '#default_value' => FALSE,
       '#suffix' => '</strong>',
     ];
     $form['maintenance_mode'] = [