Issue #3432476 by tedbow: Warn if auto-update script is running as root

automatic_updates.services.yml

@@ -56,3 +56,6 @@ services:
   Drupal\automatic_updates\CommandExecutor:
     arguments:
       $appRoot: '%app.root%'
+  Drupal\automatic_updates\Validator\ConsoleUserValidator:
+    tags:
+      - { name: event_subscriber }