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

When response schema uses additionalProperties with $ref, the generated return type for request method is dict(str, list), which fails to deserialize because list doesn't specify item types.

openapi-generator version

4.3.1, 5.0.0-beta, master

OpenAPI declaration file content or url

components:
  schemas:
    a: {type: object, additionalProperties: {$ref: '#/components/schemas/b'}}
    b: {type: array, items: {type: string}}
paths:
  /z:
    get:
      responses:
        "200":
          description: z
          content: {application/json: {schema: {$ref: '#/components/schemas/a'}}}

Generation Details

rm -rf api
docker run --rm -i --user `id -u`:`id -g` -v `pwd`:/src \
  openapitools/openapi-generator-cli generate \
    -i /src/oapi.yaml \
    -g python \
    --package-name foo \
    -o /src/api

Steps to reproduce

Observe that:

cat api/foo/api/default_api.py | grep rtype

lists a return type dict(str, list).

Related issues

I would expect this to have been fixed by #7383, but it still fails on master.

cc @spacether