[BUG] Setting v3.1.0 makes object properties AnyType

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

Setting OpenAPI version to 3.1.0 makes types of object properties AnyType.
On version 3.0.0 it works fine.
Diffs between 3.0.0 and 3.1.0: https://github.com/kawaemon/openapi-generator-310-anytype/commit/8dbb3327fe1f826d597bcd58d8c5bbdf5f8fa567

openapi-generator version

latest

OpenAPI declaration file content or url

openapi: 3.1.0

info:
  title: API
  version: 0.1.0

paths:
  '/foo':
    get:
      responses:
        '200':
          description: ok
          content:
            application/json:
              schema:
                type: object
                properties:
                  foo:
                    type: string

Generation Details

Please look at this repo:
https://github.com/kawaemon/openapi-generator-310-anytype

Steps to reproduce

openapi-generator-cli generate -g go-server -i schema.yaml -o output

Start with the provided schema.yaml and run the openapi-generator-cli command for the go-server generator. Compare the generated object property types under OpenAPI 3.1.0 with the 3.0.0 result and the linked reproduction repository; done means string properties are no longer generated as AnyType.