text: Title: I get type error if I use __root__ from pydantic while inheriting from SQLModel
  Body: ### First Check
  
  - [X] I added a very descriptive title to this issue.
  - [X] I used the GitHub search to find a similar issue and didn't find it.
  - [X] I searched the SQLModel documentation, with the integrated search.
  - [X] I already searched in Google "How to X in SQLModel" and didn't find any information.
  - [X] I already read and followed all the tutorial in the docs and didn't find an answer.
  - [X] I already checked if it is not related to SQLModel but to [Pydantic](https://github.com/samuelcolvin/pydantic).
  - [X] I already checked if it is not related to SQLModel but to [SQLAlchemy](https://github.com/sqlalchemy/sqlalchemy).
  
  ### Commit to Help
  
  - [X] I commit to help with one of those options 👆
  
  ### Example Code
  
  ```python
  from sqlmodel import SQLModel
  from pydantic import BaseModel
  
  data = [
      { "id": 1, "name": "awesome-product" }
  ]
  
  class ProductBase(SQLModel):
      name: str
  
  class ProductOut(ProductBase):
      id: int
  
  # Here 👋  If I inherit from `SQLModel`` then I get type error. However, If I inherit from `BaseModel` then I don't get error.
  # UnComment below line and comment the `SQLModel` usage to resolve the type error
  # class ProductList(BaseModel):
  class ProductList(SQLModel):
      __root__: list[ProductOut]
  
  class SomeResponse(SQLModel):
      products: ProductList
      msg: str
  
  product_list_model = ProductList.parse_obj(data)
  SomeResponse(products=product_list_model, msg="Hello world")
  ```
  
  
  ### Description
  
  I get a type error if I inherit `ProductList` model from `SQLModel` saying:
  ```
  Argument of type "SQLModel" cannot be assigned to parameter "products" of type "ProductList" in function "__init__"
    "SQLModel" is incompatible with "ProductList"
  ```
  
  However, If I use `BaseModel` from pydantic for inheritance error went away.
  
  Below line gives type error
  ```python
  class ProductList(SQLModel):
  ```
  
  Below line looks fine
  ```python
  class ProductList(BaseModel):
  ```
  
  ### Operating System
  
  Linux
  
  ### Operating System Details
  
  Ubuntu 21.10
  
  ### SQLModel Version
  
  0.0.6
  
  ### Python Version
  
  3.10.2
  
  ### Additional Context
  
  ![image](https://user-images.githubusercontent.com/47495003/159866389-61d5a36e-eada-4a8a-8068-6ac39cdd2bfd.png)
  