disambiguate set(0)

see lf-lang/lingua-franca#2280

include/reactor-cpp/port.hh

@@ -134,7 +134,8 @@ public:
   void set(const T& value) { set(make_immutable_value<T>(value)); }
   void set(T&& value) { set(make_immutable_value<T>(std::forward<T>(value))); }
   // Setting a port to nullptr is not permitted.
-  void set(std::nullptr_t) = delete;
+  template <typename V, typename = std::enable_if_t<std::is_same_v<V, std::nullptr_t>>>
+  void set(V) = delete;
   void startup() final {}
   void shutdown() final {}