[4.x] Add tokenCant() helper function to HasApiTokens

[chester-sykes]

This PR adds tokenCant() helper function to the HasApiTokens trait. It allows you to check if the accessToken does not have an ability. It is the opposite of the current tokenCan helper function.

    public function tokenCant(string $ability)
    {
        return ! $this->tokenCan($ability);
    }

It will be helpful to people who want to do something if a token does not have the ability, for example:

abort_if($user->tokenCant('foo'), 403)

I think its a bit more readable than:

abort_if(! $user->tokenCan('foo'), 403)

It won't break any existing features as this PR does not change any existing code.