style: Fix missing newline at end of files

backend/src/main/java/de/szut/casino/deposit/TransactionService.java

@@ -61,4 +61,4 @@ public class TransactionService {
         userRepository.save(user);
         transactionRepository.save(transaction);
     }
-}
+}

backend/src/main/java/de/szut/casino/deposit/WebhookController.java

@@ -67,4 +67,4 @@ public class WebhookController {
 
         return ResponseEntity.ok().body(null);
     }
-}
+}