Tiny fix in automation.h - unused return value removed (#6760)

esphome/core/automation.h

@@ -233,7 +233,7 @@ template<typename... Ts> class Automation {
  public:
   explicit Automation(Trigger<Ts...> *trigger) : trigger_(trigger) { this->trigger_->set_automation_parent(this); }
 
-  Action<Ts...> *add_action(Action<Ts...> *action) { this->actions_.add_action(action); }
+  void add_action(Action<Ts...> *action) { this->actions_.add_action(action); }
   void add_actions(const std::vector<Action<Ts...> *> &actions) { this->actions_.add_actions(actions); }
 
   void stop() { this->actions_.stop(); }