[BUG] Validation fails when anchor or alias a in the YAML file which seems correct

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?
• [x ] What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Basically the YAML is correct but the validation fails when anchors or aliases are present.

openapi-generator version

5.4.0 from homebrew

OpenAPI declaration file content or url

spec.yaml.zip to reproduce the behaviour.

Steps to reproduce

This will fail:

openapi-generator generate -i ~/Downloads/spec.yaml -g javascript -o ~/Downloads/output/

but by disabling the validation it will work

openapi-generator generate -i ~/Downloads/spec.yaml -g javascript -o ~/Downloads/output/ --skip-validate-spec

Start by extracting spec.yaml and running the reported openapi-generator command, then compare it with the same command using --skip-validate-spec. Trace the validation entry point responsible for rejecting anchors or aliases; done means the supplied specification validates and generation succeeds without that flag.