[BUG] Duplicate Enums are being generated rather than enum type being referenced in model

Created by: binaryunary

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

An enum type is generated twice instead of being generated once and then referenced from client code.

openapi-generator version

4.2.3-SNAPSHOT

OpenAPI declaration file content or url

openapi: '3.0.0'
info:
  version: 1.0.0
  title: API with Default Values
servers:
  - url: http://localhost:8080
paths:
  /test:
    post:
      operationId: testDefaults
      requestBody:
        required: true
        content:
          application/json:
            schema:
              '$ref': '#/components/schemas/Payload'
      responses:
        '200':
          description: Ok
components:
  schemas:
    Payload:
      type: object
      properties:
        stringProp:
          type: string
          default: foo
        doubleProp:
          type: number
          format: double
          default: 1.234
        enumProp:
          $ref: '#/components/schemas/EnumProp'
    EnumProp:
          type: string
          enum: [One, Two, Three]
          default: Two

Command line used for generation

docker run --rm --user "$(id -u):$(id -g)" -v ${PWD}:/local openapitools/openapi-generator-cli generate -i /local/enum.yml -g aspnetcore -o /local/out -p aspnetVersion=3.0 -Dmodels

Steps to reproduce

Save the YAML as enum.yml and run the above command.

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/3582

Suggest a fix

This seems to work as expected with -g csharp.