 combine schemas not working in 'paths'

combining schemas in path is not working
e.g. 
```
paths:
  /pets:
    patch:
      requestBody:
        content:
          application/json:
            schema:
              oneOf:
                - $ref: '#/components/schemas/Cat'
                - $ref: '#/components/schemas/Dog'
```

but it's working in

```
components:
  schemas:
  ...
```