[BUG] [scala-client]Models not generated properly if additionalProperties referenced schema is array

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

scala client generator doesn't generate the model properly if its additionalProperties refer to a schema which type is array, the referenced schema wasn't generated. The issue occurs in the both scala-sttp and scala-akka

openapi-generator version

The version 5.3.x, 5.4.x and the latest master branch (6.0.0)

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  title: stringToModelMapping
  version: "3.0.0"
paths:
  /:
    get:
      summary: Empty Route
      responses:
        "200":
          description: Good Request.
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/FreeformObjectTypes'
        "400":
          description: Bad Request.
        "403":
          description: Forbidden. Access denied.
components:
  schemas:
    SimpleModel:
      type: object
      properties:
        id:
          type: integer
          format: int64
        name:
          type: string
    ArrayModel:
      type: array
      items:
        $ref: '#/components/schemas/SimpleModel'
    FreeformObjectTypes:
      type: object
      properties:
        stringToModelMapping:
          type: object
          additionalProperties:
            $ref: '#/components/schemas/SimpleModel'
        stringToArrayModelMapping:
          type: object
          additionalProperties:
            $ref: '#/components/schemas/ArrayModel'

Generation Details

Command line used for generation

openapi-generator-cli generate \
  -g scala-sttp \
  -i name_of_file.yaml \
  -p mainPackage=myPackage \
  -o myApi

Issues in the generated client:

• No model class of referenced schema ArrayModel;
• The model class of FreeformObjectTypes refer to Seq without type.

case class FreeformObjectTypes(
  stringToModelMapping: Option[Map[String, SimpleModel]] = None,
  stringToArrayModelMapping: Option[Map[String, Seq]] = None
)

Expect:

case class FreeformObjectTypes(
  stringToModelMapping: Option[Map[String, SimpleModel]] = None,
  stringToArrayModelMapping: Option[Map[String, Seq[SimpleModel]]] = None
)

Steps to reproduce

Related issues/PRs

Suggest a fix

Run the supplied openapi-generator-cli command with the YAML declaration and inspect the generated scala-sttp models, then compare scala-akka output. Trace handling of additionalProperties referencing ArrayModel; done means ArrayModel is generated and FreeformObjectTypes uses Map[String, Seq[SimpleModel]] rather than an untyped Seq.