DX: fix phpstan issues

src/Bundle/ChillEventBundle/Entity/Event.php

@@ -160,11 +160,11 @@ class Event implements HasCenterInterface, HasScopeInterface
     }
 
     /**
-     * @return ArrayIterator|Collection|Traversable
+     * @return Collection<Participation>
      */
     public function getParticipations()
     {
-        return $this->getParticipationsOrdered();
+        return new ArrayCollection(iterator_to_array($this->getParticipationsOrdered()));
     }
 
     /**