[openapi] Types are missing when YAML spec is converted to JSON

Description

I am converting YAML spec to JSON via swagger-codegen-cli-v3. The issue is that even though the data types are defined in the source YAML schema, they are missing in the JSON output.

Swagger-codegen version

I use the latest swaggerapi/swagger-codegen-cli-v3 image.

Steps to reproduce

Here is an example.

I have a source YAML spec.yaml file like this that contains data types for properties id and type:

openapi: 3.1.0
info:
  title: Test Service
  version: 1.0.0
paths:
  "/test":
    get:
      responses:
        '200':
          content:
            application/json:
              schema:
                "$ref": "#/components/schemas/TestResponse"
components:
  schemas:
    TestResponse:
      title: TestResponse
      type: object
      required:
        - type
        - id
      properties:
        type:
          type: string
        id:
          type: number

I run the following command in the spec.yaml file directory:
docker run -v $(pwd):/api swaggerapi/swagger-codegen-cli-v3 generate -l openapi -i /api/spec.yaml -o /api/gen -DoutputFile=api.json

and get the JSON result without data types (string and number keywords are missing):

{
  "openapi" : "3.1.0",
  "info" : {
    "title" : "Test Service",
    "version" : "1.0.0"
  },
  "servers" : [ {
    "url" : "/"
  } ],
  "paths" : {
    "/test" : {
      "get" : {
        "responses" : {
          "200" : {
            "content" : {
              "application/json" : {
                "schema" : {
                  "$ref" : "#/components/schemas/TestResponse"
                }
              }
            }
          }
        }
      }
    }
  },
  "components" : {
    "schemas" : {
      "TestResponse" : {
        "title" : "TestResponse",
        "required" : [ "id", "type" ],
        "properties" : {
          "type" : { },
          "id" : { }
        }
      }
    }
  }
}

Command line used for generation

docker run -v $(pwd):/api swaggerapi/swagger-codegen-cli-v3 generate -l openapi -i /api/spec.yaml -o /api/gen -DoutputFile=api.json

Related issues/PRs

Haven't found a related issue.

Reproduce the conversion with spec.yaml using the documented swagger-codegen-cli-v3 Docker command and inspect the OpenAPI generator entry point. The JSON output in /api/gen/api.json should preserve the string and number types for TestResponse.properties.type and TestResponse.properties.id.