Describe the bug
When using OpenAPI discriminator mapping with non-string values (for example integer enum values), generated models treat the discriminator field as a string.
As a result, the generated type for the discriminator does not match the OpenAPI schema type and can break runtime validation and type checking.

To Reproduce

Example schema:

{
  "openapi": "3.0.3",
  "info": {
    "title": "Minimal Integer Discriminator",
    "version": "1.0.0"
  },
  "paths": {},
  "components": {
    "schemas": {
      "Base": {
        "oneOf": [
          { "$ref": "#/components/schemas/Foo" },
          { "$ref": "#/components/schemas/Bar" }
        ],
        "discriminator": {
          "propertyName": "kind",
          "mapping": {
            "1": "#/components/schemas/Foo",
            "2": "#/components/schemas/Bar"
          }
        }
      },
      "Foo": {
        "type": "object",
        "properties": {
          "kind": {
            "type": "integer",
            "enum": [1]
          }
        },
        "required": ["kind"]
      },
      "Bar": {
        "type": "object",
        "properties": {
          "kind": {
            "type": "integer",
            "enum": [2]
          }
        },
        "required": ["kind"]
      }
    }
  }
}

Used commandline:

$ datamodel-codegen --input example.json --input-file-type openapi --output model.py

Output:

from __future__ import annotations

from enum import IntEnum
from typing import Literal

from pydantic import BaseModel, Field, RootModel


class Kind(IntEnum):
    integer_1 = 1


class Foo(BaseModel):
    kind: Literal['1']


class Kind1(IntEnum):
    integer_2 = 2


class Bar(BaseModel):
    kind: Literal['2']


class Base(RootModel[Foo | Bar]):
    root: Foo | Bar = Field(..., discriminator='kind')

Expected behavior
The discriminator field type should follow the schema type (integer), for example using integer literal values for each subtype (such as 1 and 2), instead of string-based discriminator typing.

Version:

• OS: macOS
• Python version: 3.13.11
• datamodel-code-generator version: 0.55.1.dev6+g7e1a5c751

Additional context
OpenAPI 3.1 Discriminator Object states:

Mapping keys MUST be string values, but tooling MAY convert response values to strings for comparison.

I understand this as: discriminator mapping keys to be string values, but the discriminator properties itself does not have to be string values.