Resolve #3462503 "Unknown method getcontents"

Closes #3462503

src/Controller/LearningPathMembershipController.php

@@ -523,9 +523,8 @@ class LearningPathMembershipController extends ControllerBase {
       throw new NotFoundHttpException();
     }
 
-    $content = $group->getContent();
-    /** @var \Drupal\group\Entity\GroupContentInterface $item */
-    foreach ($content as $item) {
+    $items = $group->getRelationships();
+    foreach ($item as $items) {
       $entity = $item->getEntity();
       $type = $entity->getEntityTypeId();
       $bundle = $entity->bundle();