[12.x] Fix type nullability on PasswordBroker.events property

[jnoordsij]

Per constructor, this property may be null:

framework/src/Illuminate/Auth/Passwords/PasswordBroker.php

Lines 37 to 49 in c0c2441

	/**
	* Create a new password broker instance.
	*
	* @param \Illuminate\Auth\Passwords\TokenRepositoryInterface $tokens
	* @param \Illuminate\Contracts\Auth\UserProvider $users
	* @param \Illuminate\Contracts\Events\Dispatcher|null $dispatcher
	*/
	public function __construct(#[\SensitiveParameter] TokenRepositoryInterface $tokens, UserProvider $users, ?Dispatcher $dispatcher = null)
	{
	$this->users = $users;
	$this->tokens = $tokens;
	$this->events = $dispatcher;
	}

It is also called in a nullsafe manner:

framework/src/Illuminate/Auth/Passwords/PasswordBroker.php

Line 84 in c0c2441

$this->events?->dispatch(new PasswordResetLinkSent($user));