[9.x] Allow instance of Enum pass Enum Rule

[cbaconnier]

Given this scenario, the validation for country currently fail as it expect the value of CountryEnum.
Laravel will automatically cast the enum instance when saving the model, therefore, it should be safe to validate by it's instance.

$action = new CreateNewUser();

$action->create([
    'country' => CountryEnum::CH,
    'email'   => 'john.doe@example.org',
]);

public function create(array $input)
{
    Validator::make($input, [
        'country' => ['required',  Enum(CountryEnum::class)],
        'email'   => [...],
    ])->validate();
}