Issue #3436741 make Automatic Updates Extension stable

Closes #3436741

automatic_updates_extensions/src/Form/UpdateReady.php

@@ -136,6 +136,12 @@ final class UpdateReady extends UpdateFormBase {
       '#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']),
       '#suffix' => '</strong>',
     ];
+    $form['warning'] = [
+      '#title' => $this->t('Warning: Updating contribute projects may leave your site inoperable.'),
+      '#type' => 'checkbox',
+      '#required' => TRUE,
+      '#default_value' => FALSE,
+    ];
     $form['maintenance_mode'] = [
       '#title' => $this->t('Perform updates with site in maintenance mode (strongly recommended)'),
       '#type' => 'checkbox',