Describe the bug
A model that defines a string enum with 3 options YES/NO/NOT_APPLICABLE is turned into a bool enum with one string option.
To Reproduce

Example schema:

openapi: "3.0.0"
info:
  title: "test"
  description: "test"
  version: "0.1"

components:
  schemas:
    HaveHaveNots:
      type: "object"
      properties:
        hasIt:
          type: string
          enum:
            - YES
            - NO
            - NOT_APPLICABLE
          example: YES

This results in the following class:

from __future__ import annotations

from enum import Enum
from typing import Optional

from pydantic import BaseModel, Field


class HasIt(Enum):
    True_ = True
    False_ = False
    NOT_APPLICABLE = 'NOT_APPLICABLE'


class HaveHaveNots(BaseModel):
    hasIt: Optional[HasIt] = Field(None, example=True)

Used commandline:

$ datamodel-codegen --input test.yaml --output test.py

Expected behavior

I would have expected the class to look like this (just strings):

class HasIt(Enum):
    YES = "YES"
    NO = "NO"
    NOT_APPLICABLE = 'NOT_APPLICABLE'


class HaveHaveNots(BaseModel):
    hasIt: Optional[HasIt] = Field(None, example="YES")

Version:

• OS: Mac Sonoma
• Python version: 3.11
• datamodel-code-generator version: 0.25.1

Additional context
Add any other context about the problem here.