dev/core#2178 Fix regression on adding contacts to a newly created group

https://github.com/civicrm/civicrm-core/pull/18967 from Seamus Lee

civicrm/CRM/Group/Controller.php

@@ -15,6 +15,7 @@
  * @copyright CiviCRM LLC https://civicrm.org/licensing
  */
 class CRM_Group_Controller extends CRM_Core_Controller {
+  protected $entity = 'Contact';
 
   /**
    * Class constructor.
@@ -52,6 +53,7 @@ class CRM_Group_Controller extends CRM_Core_Controller {
 
     // add all the actions
     $this->addActions($uploadDir, $uploadNames);
+    $this->set('entity', $this->entity);
   }
 
   /**