Enable sync transport in messenger configuration (#1464)

Very little downside to enabling by default, as it's (almost) the same as not sending something through a transport at all.

symfony/messenger/6.0/config/packages/messenger.yaml

@@ -7,7 +7,7 @@ framework:
             # https://symfony.com/doc/current/messenger.html#transport-configuration
             # async: '%env(MESSENGER_TRANSPORT_DSN)%'
             # failed: 'doctrine://default?queue_name=failed'
-            # sync: 'sync://'
+            sync: 'sync://'
 
         routing:
             # Route your messages to the transports