Duplicate key in Enum when using both lowercase and uppercase strings

Describe the bug

enums are case-sensitive in OpenAPI spec[1] but the openapi generator does not treat them that way. When I try to use both lowercase and uppercase values in enum like so:

components:
  schemas:
    DocumentType:
      type: string
      enum: [txt, TXT]

I get this error:

Traceback (most recent call last):

  File "/Users/xxx/.local/bin/openapi-python-client", line 8, in <module>
    sys.exit(app())
             ^^^^^

  File "/Users/xxx/.local/pipx/venvs/openapi-python-client/lib/python3.12/site-packages/openapi_python_client/cli.py", line 175, in update
    errors = update_existing_client(
             ^^^^^^^^^^^^^^^^^^^^^^^

  File "/Users/xxx/.local/pipx/venvs/openapi-python-client/lib/python3.12/site-packages/openapi_python_client/__init__.py", line 336, in update_existing_client
    project = _get_project_for_url_or_path(
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  File "/Users/xxx/.local/pipx/venvs/openapi-python-client/lib/python3.12/site-packages/openapi_python_client/__init__.py", line 295, in _get_project_for_url_or_path
    openapi = GeneratorData.from_dict(data_dict, config=config)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  File "/Users/xxx/.local/pipx/venvs/openapi-python-client/lib/python3.12/site-packages/openapi_python_client/parser/openapi.py", line 503, in from_dict
    schemas = build_schemas(components=openapi.components.schemas, schemas=schemas, config=config)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  File "/Users/xxx/.local/pipx/venvs/openapi-python-client/lib/python3.12/site-packages/openapi_python_client/parser/properties/__init__.py", line 386, in build_schemas
    schemas = _create_schemas(components=components, schemas=schemas, config=config)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  File "/Users/xxx/.local/pipx/venvs/openapi-python-client/lib/python3.12/site-packages/openapi_python_client/parser/properties/__init__.py", line 307, in _create_schemas
    schemas_or_err = update_schemas_with_data(ref_path=ref_path, data=data, schemas=schemas, config=config)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  File "/Users/xxx/.local/pipx/venvs/openapi-python-client/lib/python3.12/site-packages/openapi_python_client/parser/properties/schemas.py", line 114, in update_schemas_with_data
    prop, schemas = property_from_data(
                    ^^^^^^^^^^^^^^^^^^^

  File "/Users/xxx/.local/pipx/venvs/openapi-python-client/lib/python3.12/site-packages/openapi_python_client/parser/properties/__init__.py", line 178, in property_from_data
    return EnumProperty.build(
           ^^^^^^^^^^^^^^^^^^^

  File "/Users/xxx/.local/pipx/venvs/openapi-python-client/lib/python3.12/site-packages/openapi_python_client/parser/properties/enum_property.py", line 124, in build
    values = EnumProperty.values_from_list(value_list)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  File "/Users/xxx/.local/pipx/venvs/openapi-python-client/lib/python3.12/site-packages/openapi_python_client/parser/properties/enum_property.py", line 203, in values_from_list
    raise ValueError(f"Duplicate key {key} in Enum")

ValueError: Duplicate key TXT in Enum

OpenAPI Spec File

see above

Desktop (please complete the following information):

• OS: macOS 15.x
• Python Version: 3.12
• openapi-python-client version 0.19.1

Bắt đầu với openapi_python_client/parser/properties/enum_property.py, đặc biệt là values_from_list, sử dụng schema được cung cấp với các giá trị enum txt và TXT để tái hiện lỗi. Công việc được hoàn tất khi các giá trị enum khác nhau về chữ hoa chữ thường này được chấp nhận mà không có lỗi khóa trùng lặp và hành vi này được bao phủ bởi một test phù hợp.