[BUG] python-fastapi generator problem with enumeration.

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

openapi-generator-cli -g python-fastapi generator cannot generate the valid enum class.

openapi-generator version

5.2.0

OpenAPI declaration file content or url

components:
  schemas:
    example.test_enumeration:
      type: string
      title: This is Enum
      enum:
        - ENUM_1
        - ENUM_2
        - ENUM_3

Generation Details

# coding: utf-8

from __future__ import annotations
from datetime import date, datetime  # noqa: F401

import re  # noqa: F401
from typing import Any, Dict, List, Optional  # noqa: F401

from pydantic import AnyUrl, BaseModel, EmailStr, validator  # noqa: F401


class ExampleTestEnumeration(BaseModel):
    """NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).

    Do not edit the class manually.

    ExampleTestEnumeration - a model defined in OpenAPI

    """


ExampleTestEnumeration.update_forward_refs()

Steps to reproduce

Related issues/PRs

Start by running the python-fastapi generator with the provided YAML schema and inspect the generated ExampleTestEnumeration class. Compare it with the enum values in the input; done means the generator produces a valid Python enum model representing ENUM_1, ENUM_2, and ENUM_3.