Fix type nullability on PasswordBroker.events property (#55097)

Per constructor, this property may be null.

Author: jnoordsij

src/Illuminate/Auth/Passwords/PasswordBroker.php

@@ -30,7 +30,7 @@ class PasswordBroker implements PasswordBrokerContract
     /**
      * The event dispatcher instance.
      *
-     * @var \Illuminate\Contracts\Events\Dispatcher
+     * @var \Illuminate\Contracts\Events\Dispatcher|null
      */
     protected $events;