chore: remove redundant instance check flagged by phpstan

src/Form/Model/BookingDto.php

@@ -379,10 +379,8 @@ class BookingDto
         }
 
         foreach ($this->participants as $participant) {
-            if ($participant instanceof ParticipantDto) {
-                // Temporary cleanup for older serialized participants restored from session.
-                $participant->normalizeBodyDimensions();
-            }
+            // Temporary cleanup for older serialized participants restored from session.
+            $participant->normalizeBodyDimensions();
         }
 
         // Old sessions (before c373a989) still carry a full Travel object;