[BUG] nullable innerEnum not generated in aspnetcore template

Description

When an innerEnum is defined and that enum is nullable, the enum class itself will not be defined.

Ex: public MyEnumEnum? MyEnum { get; set; } where the MyEnumEnum class is never defined. This results in code that will not compile.

In the spec below, my_enum evaluates to complexType string? (seen in model debugging).

In the template, {{>enumClass}} is only run when complexType is false. https://github.com/OpenAPITools/openapi-generator/blob/c2472b03b63fa61a3d7e5b086f36c1bd48d0ee4c/modules/openapi-generator/src/main/resources/aspnetcore/3.0/model.mustache#L52-L63

I don't know why it is only generated when complexType is false, and I'm not sure what might / will break if that condition is removed.

openapi-generator version

7.7.0

OpenAPI declaration file content or url

openapi: "3.0.0"
info:
  version: 1.0.0
  title: Swagger Petstore
servers: []
paths: {}
components:
  schemas:
    Pet:
      type: object
      properties:
        my_enum:
          type: string
          nullable: true
          enum:
            - "value1"

Generation Details

generate --generator-name aspnetcore -i spec.yml \
--additional-properties nullableReferenceTypes=true

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)

Start with modules/openapi-generator/src/main/resources/aspnetcore/3.0/model.mustache, especially lines 52-63, and reproduce the issue using the supplied spec and generation command with the aspnetcore generator. Compare the generated output for the nullable enum and verify that the enum class is defined and the generated C# code compiles.