Adapt exception.cpp

rt/test/exceptions.cpp

@@ -25,7 +25,7 @@ Join<void> fail_join() {
 }
 
 Join<void> join(int max) {
-  std::vector<Future<Fork<int>::promise_type>> v;
+  std::vector<Future<int>> v;
   for (int i = 0; i < max; i++) {
     v.push_back(co_await fork(fib()));
   }