Without a connection to the actuator, the wastegate never gets a signal to open. So the turbo just keeps building boost, until the engine spits 6 pistons out through the bonnet of the car.
With that hose venting boost to atmosphere, the wastegate doesn't get the full boost signal (it's acting like a bleed valve), so you risk getting same result as above.
In the worst case, that hose should be plugged (a small bolt is sufficient). In the best case, it probably should be connected to the wastegate (or boost controller).