Describe the bug
An OpenAPI schema with a self-referencing object with a discriminated union produces code with undefined variables for all output model types except pydantic v1 BaseModel.

To Reproduce

Example schema:

---
openapi: 3.1.0
components:
  schemas:
    Bar:
      type: object
      properties:
        kind:
          const: Bar
      required:
      - kind
    Foo:
      type: object
      properties:
        kind:
          const: Foo
        children:
          type: array
          items:
            oneOf:
            - "$ref": "#/components/schemas/Foo"
            - "$ref": "#/components/schemas/Bar"
            discriminator:
              propertyName: kind
              mapping:
                Foo: "#/components/schemas/Foo"
                Bar: "#/components/schemas/Bar"
          title: Children
      required:
      - children
      - kind

Used commandline:

$ datamodel-codegen --output-model-type typing.TypedDict

Output:

from __future__ import annotations

from typing import List, Union

from typing_extensions import NotRequired, TypedDict


class Bar(TypedDict):
    kind: NotRequired[str]


Children = Union[Foo, Bar]  # Foo is undefined!


class Foo(TypedDict):
    kind: NotRequired[str]
    children: List[Children]

Similar error happens for other output model types. Only pydantic v1 works because Foo is a variable annotation, rather than in a Union in a type alias.

Expected behavior
Reference to Foo properly turned into forward reference

Version:

• OS: Ubuntu 20.04
• Python version: 3.12
• datamodel-code-generator version: 0.25.3

Additional context
It works properly if the discriminator is removed from the schema.