[BUG] Generator try to use oneOf* model but does not create it

Created by: Adi1231234

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

On oneOf usage in openAPI declaration the generator try to use oneOf* model but does not create it in any language

openapi-generator version

5.0.1

OpenAPI declaration file content or url

{
  "openapi": "3.0.0",
  "info": {
    "title": "service",
    "description": "API",
    "version": "1.0",
    "contact": {}
  },
  "tags": [],
  "servers": [],
  "components": {
    "schemas": {
      "Category": {
        "type": "object",
        "properties": {
          "name": { "type": "string" },
          "parentCategoryId": { "type": "number" }
        },
        "required": ["name", "parentCategoryId"]
      },
      "GetManyCategoryResponseDto": {
        "type": "object",
        "properties": {
          "data": {
            "type": "array",
            "items": { "$ref": "#/components/schemas/Category" }
          },
          "count": { "type": "number" },
          "total": { "type": "number" },
          "page": { "type": "number" },
          "pageCount": { "type": "number" }
        },
        "required": ["data", "count", "total", "page", "pageCount"]
      }
    }
  },
  "paths": {
    "/categories": {
      "get": {
        "operationId": "getManyBaseCategoriesControllerCategory",
        "summary": "Retrieve many Category",
        "parameters": [
          {
            "name": "fields",
            "description": "Selects resource fields",
            "required": false,
            "in": "query",
            "schema": { "type": "array", "items": { "type": "string" } },
            "style": "form",
            "explode": false
          }
        ],
        "responses": {
          "200": {
            "description": "Get many base response",
            "content": {
              "application/json": {
                "schema": {
                  "oneOf": [
                    {
                      "$ref": "#/components/schemas/GetManyCategoryResponseDto"
                    },
                    {
                      "type": "array",
                      "items": { "$ref": "#/components/schemas/Category" }
                    }
                  ]
                }
              }
            }
          }
        },
        "tags": ["Categories"]
      }
    }
  }
}

Generation Details

Steps to reproduce

execute - java -jar openapi-generator-cli.jar generate -i categories.swagger -o out -g (any language)

then at api/categories_api the generated function is:

Future<Response<OneOfGetManyCategoryResponseDtoarray>> getManyBaseCategoriesControllerCategory({ 
  BuiltList<String> fields,
})

the problem is that OneOfGetManyCategoryResponseDtoarray class does not exist in any file.

Related issues/PRs

#3965 - Similar a bit

Suggest a fix