chore: fix phpstan errors

src/Controller/Booking/Create/Step2ParticipantController.php

@@ -124,6 +124,7 @@ class Step2ParticipantController extends AbstractController
         );
     }
 
+    /** @param FormInterface<mixed> $form */
     private function renderParticipantForm(
         FormInterface $form,
         int $index,
@@ -157,6 +158,7 @@ class Step2ParticipantController extends AbstractController
         return $bookingDto;
     }
 
+    /** @return FormInterface<mixed> */
     private function createParticipantForm(BookingDto $bookingDto, int $index): FormInterface
     {
         $wrapper = $this->participantFormSupportService->createParticipantEditDto($bookingDto, $index);