fix: make selection of transportation services mandatory

src/Form/Model/ParticipantData.php

@@ -40,8 +40,13 @@ class ParticipantData
     public array $skiPass = [];
     public array $board = [];
     public array $rentals = [];
+
+    #[Assert\NotNull(message: 'Bitte angeben')]
     public ?Service $transportationServiceTo = null;
+
+    #[Assert\NotNull(message: 'Bitte angeben')]
     public ?Service $transportationServiceFro = null;
+
     public ?Pickup $pickup = null;
 
     #[Assert\Callback]