fix: post hook invalid when symfony messenger sender throws exception

I still need to validate that this solves the problem but looking at the code this is the only thing that makes sense to me to solve it.

```
Symfony\Component\Messenger\Bridge\Amqp\Transport\AmqpTransport::send(): OpenTelemetry: post hook invalid signature, class=Symfony\Component\Messenger\Bridge\Amqp\Transport\AmqpTransport function=send
```

src/Instrumentation/Symfony/src/MessengerInstrumentation.php

@@ -150,7 +150,7 @@ public static function register(): void
             post: static function (
                 SenderInterface $sender,
                 array $params,
-                Envelope $result,
+                ?Envelope $result,
                 ?\Throwable $exception
             ): void {
                 $scope = Context::storage()->scope();