Does not support $ref properties

### Prerequisites

- [X] I have written a descriptive issue title
- [X] I have searched existing issues to ensure the bug has not already been reported

### Fastify version

4.28.0

### Plugin version

2.6.0

### Node.js version

20.15.0

### Operating system

Linux

### Operating system version (i.e. 20.04, 11.3, 10)

ubuntu

### Description

The plugin is failing the schema validation when there is a `$ref` in the `response` object.

In the sample code provided you can see it working without the plugin and also when the `response` doesn't get a `$ref`.

I'm using TypeBox for schema generation, but it doesn't matter. Even if you write it a plain object it continues failing.

### Link to code that reproduces the bug

https://github.com/jpenna/fastify-response-error

### Expected Behavior

It shouldn't crash the build.