[BUG] [GO] Model generates incorrectly for objects with properties and OneOf types at the same level

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

We have a spec that contains properties at the same level as a OneOf object. The generated model does not match the spec.

openapi-generator version

openapitools/openapi-generator-cli:5.1.1

OpenAPI declaration file content or url

The part of spec in question is below. Full spec is also attached in the gist below

CustomerName:
      type: object
      required:
        - display_name
      properties:
        display_name:
          description: Customer's common or display name
          $ref: '#/components/schemas/DisplayNameType'
      oneOf:
        - type: object
          properties:
            individual_name:
              $ref: '#/components/schemas/IndividualName'
        - type: object
          properties:
            business_name:
              $ref: '#/components/schemas/BusinessName'

https://gist.github.com/saikris12/883abef8ad8b7e0544b1d60f0bb3d92f

Generation Details

docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli:latest generate
-i /local/swagger/customer.yaml
-g go
-o /local/partners/clients/customer
--additional-properties=packageName=customer,isGoSubmodule=true,enumClassPrefix=true,generateInterfaces=true

Steps to reproduce

Generate the go client using the spec above. It should generate the model_create_customer_request.go file with the below model. The display_name which is under the CustomerName object never gets generated since its on the same level as the OneOf.

type CustomerName struct {
	CustomerNameOneOf *CustomerNameOneOf
	CustomerNameOneOf1 *CustomerNameOneOf1
}

Related issues/PRs

No

Suggest a fix

I tried overriding the mustache template model_oneof.mustache, but I am having issues with the Marshal function. I am not sure how I can marshal the display name along with the OneOf field. I am expecting the name field to be as below :

"name": {
    "display_name": "string",
    "individual_name": {
      "first_name": "string",
      "middle_name": "string",
      "last_name": "string"
    }
  },

Run the provided Docker generation command with the linked OpenAPI spec, then inspect model_oneof.mustache and the generated model_create_customer_request.go file. Confirm how the shared display_name property is omitted and how the generated Marshal behavior handles the OneOf fields. Done means the model includes display_name and produces the expected JSON alongside the selected OneOf value.