"no compatible schema found" error. Can the tool evaluate schema $refs under the top of the path?

### tfplugingen-openapi CLI version

v0.3.0

### OpenAPI Spec File

```YAML
'/users/{user-id}':
get:
responses:
2XX:
description: Retrieved entity
content:
application/json:
schema:
$ref: '#/components/schemas/(reference path)'
```

### Generator Config

```YAML
provider:
name: (name)
data_sources:
users:
read:
path: /users/{user-id}
method: GET
```

### Expected Behavior

Evaluate the reference schema and generate the provider code spec.

### Actual Behavior

Failed with error:
```
time=(redacted) level=WARN msg="skipping data source schema mapping" data_source=users err="no compatible schema found"
```

### Additional Information

Hi team,

The OpenAPI spec for the system I am trying to create a provider for has a reference to the response object schema at the top of the schema block. Does the tool support this?
I saw on the DESIGN.md that it does support expanding a $ref tag, but it was inside of a nested schema.

Or perhaps I'm doing something wrong here?

Cheers,
Harry

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