[BUG][Golang][Client] Response JSON array of object not handled in spec 2.0 but works in spec 3.0

Created by: grokify

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

When using an OAS 2.0 spec with a response that is an array of object, the generated code attempts to return a map[string]interface{} which runs into an error when the array is unmarshaled.

OAS 2.0 results in the following method signature which attempts to return a map[string]interface{}

func (a *LocalesApiService) GetAllLocales(ctx context.Context) (map[string]interface{}, *http.Response, error) {

This results in the following error:

json: cannot unmarshal array into Go value of type map[string]interface {}

Using an OAS 3.0 spec works as expected. It returns a []Locale as expected:

func (a *LocalesApiService) GetAllLocales(ctx context.Context) ([]Locale, *http.Response, error) {

openapi-generator version

4.1.0-SNAPSHOT, master branch

OpenAPI declaration file content or url

Non-working 2.0 spec: https://github.com/grokify/go-ringcentral-engage/blob/fd5a68df4d1612de69bed7e35c10ceb337a8da32/codegen/partial-specs_v2.0.0/openapi-spec_locales.json

Working 3.0 spec: https://github.com/grokify/go-ringcentral-engage/blob/fd5a68df4d1612de69bed7e35c10ceb337a8da32/codegen/partial-specs_v3.0.0/openapi-spec_locales.json

Command line used for generation

$ java -jar openapi-generator-cli.jar generate -i partial-specs_v3.0.0/openapi-spec_locales.json -g go -o engagedigital --package-name engagedigital

Steps to reproduce

Build a SDK against the linked specs.

Related issues/PRs

https://github.com/grokify/go-ringcentral-engage/issues/2

Suggest a fix

Make it work like the OAS 3.0 spec.