[BUG] go-server: Unable to return a *os.File in the body as simple binary data upon get request

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?
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Description

I am trying to create an api get response, where part of the body is a full file content, encoded as a simple octet array, or plain binary data. When I define a corresponding endpoint uri that returns as part of the http response a binary file, I only receive an empty response for that file section.
I would expect it to return some sort of binary content within the response.

openapi-generator version

5.4.0
No idea if it is a regression.

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  description: simple service
  license:
    name: Proprietary
  title: some title
  version: 1.0.0
externalDocs:
  description: Design file can be found in wiki
  url: https://somewhere.else/wiki
servers:
- url: http://localhost:9091/manager/v1
tags:
- name: manager
  description: TODO add a description
  
paths:
  /schemas:
    get:
      operationId: SchemaList
      responses:
        "200":
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/SchemaName'
          description: successful
        "500":
          description: internal server error
        "503":
          description: service unavailable          
      summary: get list of schema families
      description: gets the top level overview over families of schemas
      tags:
        - schema
  '/schema/{family}':
    get:
      operationId: FamilyList
      parameters:
        - name: family
          in: path
          description: name of the family
          required: true
          schema:
            type: string
      responses:
        "200":
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/SchemaName'
          description: successful
        "500":
          description: internal server error
        "503":
          description: service unavailable          
      summary: get list of schemas belonging to a schema family
      tags:
        - schema
  '/schema/{family}/{version}':
    get:
      operationId: SchemaFile
      parameters:
        - name: family
          in: path
          description: name of the family
          required: true
          schema:
            type: string
        - name: version
          in: path
          description: version of file within family of schemas
          required: true
          schema:
            type: string
      responses:
        "200":
          content:
            application/octet-stream:
              schema:
                $ref: '#/components/schemas/SchemaFile'
          description: successful
        "500":
          description: internal server error
        "503":
          description: service unavailable          
      summary: get schema of a certain family in a certain version
      tags:
        - schema  
components:
  schemas:
    SchemaName:
      title: SchemaName
      description: representation of a schema family
      type: object
      required:
        - name
      properties:
        name:
          type: string
          example: "myLittleSchema"
    SchemaFile:
      title: SchemaFile
      description: a schema file, either a single file or a archive (e.g. a .zip)
      type: object
      required:
        - name
        - file
      properties:
        name:
          description: filename
          type: string
          example: "yourFile.txt"
        file:
          description: the file itself
          type: string
          format: binary

Generation Details

Generated a go-server with a call of:
java -jar openapi-generator-cli.jar generate -i rest_api.yml -g go-server -o .

In the generated code file api_schema_service.go I extended the following code section:

const fakeFile string = "/home/user/existingfile.txt"

// SchemaFile - get schema of a certain family in a certain version
func (s *SchemaApiService) SchemaFile(ctx context.Context, family string, version string) (ImplResponse, error) {
	file, err := os.Open(fakeFile)
	fmt.Printf("name: %s\nfile: %v\nerr: %v\n", fakeFile, file, err)
	if err != nil {
		return Response(500, nil), errors.New("file not found")
	}
	return Response(http.StatusOK, SchemaFile{Name: fakeFile, File: file}), nil
}

Running this code and requesting a get from this with curl results in:

$ curl -X 'GET' 'http://localhost:8080/manager/v1/schema/A/b' -H 'accept: application/octet-stream'
{"name":"/home/user/existingfile.txt","file":{}}

I would expect the field "file" to contain something. The file '/home/user/existingfile.txt' exists and contains the following content:

$ cat /home/user/existingfile.txt 
Hello, my name is test file, and welcome to openapi

Steps to reproduce

Create a .yml with the contents above, and rerun the commands specified above.

Related issues/PRs

None

Suggest a fix

No idea.

Start with the generated api_schema_service.go and the OpenAPI SchemaFile declaration, then reproduce the request using the supplied YAML, generation command, and curl example. Trace how the go-server response serializes the os.File field; done means the file field returns the expected binary content instead of an empty object.