fix: add cast to void to silence compiler warning in case of empty parameter list

include/sdbus-c++/MethodResult.h

@@ -76,7 +76,7 @@ namespace sdbus {
     {
         assert(call_.isValid());
         auto reply = call_.createReply();
-        (reply << ... << results);
+        (void)(reply << ... << results);
         reply.send();
     }