fix: stuck messages

Conduit did not send the event in /sync because of a race condition.
There is a brief moment in time where Conduit accepted the event, but
did not store it yet. So when the client /syncs it updates the since
token without sending the event. I hope I fixed it by significantly
shortening the race-condition period.

src/ruma_wrapper.rs

@@ -320,6 +320,7 @@ where
             }),
             Err(e) => {
                 warn!("{:?}", e);
+                // Bad Json
                 Failure((Status::new(583), ()))
             }
         }