text: Title: Can't get a basic Schema to work
  Body: I'm trying to get the most basic of schema to work, i.e:
  
  ```
  from ninja import Router, Schema
  
  class SimpleSchemaOut(Schema):
      name: str
  
  @router.get('/simple')
  def simple(request, response=SimpleSchemaOut):
      return {"name": "Foo"}
  ```
  
  With this in place, if I try to hit `/api/demo/openapi.json` I get the following error:
  
  ```
  TypeError at /api/demo/openapi.json
  Object of type 'ResolverMetaclass' is not JSON serializable
  
  
  
  Request Method: | GET
  Request URL: http://localhost:8080/api/demo/openapi.json
  Djagno Version: 2.2.21
  Exception Type: TypeError
  Exception Value: Object of type 'ResolverMetaclass' is not JSON serializable
  Exception Location: pydantic/json.py in pydantic.json.pydantic_encoder, line 97
  ```
  
  
  Any help would be appreciated!