This allows people to extend the When attribute with something like this:

```php
use Attribute;
use Symfony\Component\DependencyInjection\Attribute\When;

#[Attribute(Attribute::TARGET_CLASS | Attribute::TARGET_METHOD | Attribute::TARGET_FUNCTION | Attribute::IS_REPEATABLE)]
final class Exclude extends When
{
    public function __construct()
    {
        parent::__construct('never');
    }
}
```

Then they can use `#[Exclude]` instead of `#[When(env: 'never')]`.

References:
- symfony#46643
- symfony#46655