ref nullable false

Minimal repoduce:

```json
{
"openapi": "3.1.0",
"info": {
"title": "Test",
"description": "Test",
"version": "1.0"
},
"components": {
"schemas": {
"Test": {
"type": "object",
"properties": {
"A": {
"$ref": "#/components/schemas/TestB",
"nullable": true
}
}
},
"TestB": {
"type": "object",
"properties": {
"join": {
"type": "string"
}
}
}
}
}
}
```

Test case

```php

components->schemas['Test']->properties['A']->nullable == true, 'Property A is not null');
```

Reproduce the issue with the provided openapi.json and PHP script using Reader::readFromJsonFile. Start by tracing how the referenced TestB schema is loaded for Test.properties.A, then verify that its nullable value is preserved. Done means the supplied assertion passes for the OpenAPI 3.1 example.

Written by the indexing model from the issue text.