text: Title: Field names which begins and ends with underscores being prefixed with `field`
  Body: **Describe the bug**
  
  There was a PR some time ago: https://github.com/koxudaxi/datamodel-code-generator/pull/962
  It restricts usage of protected and private variables, but it doesn't consider variables with double-underscores on both sides, e.g. `__version__`. 
  Such variables are supported by pydantic and you can access them without any problems.
  
  **To Reproduce**
  
  Example schema:
  ```json
  
  {
      "title": "Event",
        "properties": {
          "__version__": {
            "type": "string",
            "title": "Event version"
          }
      }
  }
  
  
  ```
  
  Used commandline:
  ```
  $ datamodel-codegen --input event.json --output event.py
  ```
  
  ** Actual behavior **
  
  ```python
  
  class Event(BaseModel):
      field__version__: Optional[str] = Field(
          None, alias='__version__', title='Event version'
      )
  
  ```
  
  **Expected behavior**
  
  ```python
  
  class Event(BaseModel):
      __version__: Optional[str] = Field(
          None, alias='__version__', title='Event version'
      )
  
  ```
  
  **Version:**
   - OS: MacOS
   - Python version: 3.11
   - datamodel-code-generator version: 0.21.1
  