References to incorrect components should be considered invalid

## Expected
Referencing a component that does not meet the criteria an object requires should be considered invalid.

### Example
A Response object referencing a component that does not contain a "description" should be considered invalid.


### Reasoning
["description" is a **REQUIRED** property for a Response object](https://spec.openapis.org/oas/v3.1.0#response-object).

## Actual
Referencing a component that does not meet the criteria an object requires is considered valid.

### Example

```php
$api = Reader::readFromJson(<<validate()); // bool(true)
```

Start with the Reader::readFromJson example and the $api->validate() call, then trace how the response $ref is resolved and validated against the referenced component. Add a regression case for a response referencing an invalid schema component; done means validation rejects the example instead of returning true.

Vom Indexierungsmodell aus dem Issue-Text verfasst.