refactor(systems/github): save received item count before local post-filter

src/main/java/de/hftstuttgart/unifiedticketing/systems/github/GithubFilter.java

@@ -190,6 +190,8 @@ public class GithubFilter extends Filter<GithubTicket, GithubFilter>
             else throw new DeserializationException(e);
         }
 
+        lastReceivedItemCount = tr.size();
+
         logger.log(Level.FINER, "starting query post filter");
         Stream<GithubTicketResponse> ticketStream = tr.stream();