Define property.

src/Routing/FixityCheckRouteSubscriber.php

@@ -21,6 +21,13 @@ class FixityCheckRouteSubscriber extends RouteSubscriberBase {
    */
   protected $fixity;
 
+  /**
+   * The entity type manager service.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected EntityTypeManagerInterface $entityTypeManager;
+
   /**
    * Subscriber for Fixity Check routes.
    *