[BUG] Schema $ref with same name is not producing models properly

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

My schema definition are spread across multiple files and they are cross reference(using $ref). In these files there is one schema with same name. I have 5 such instances

When i run code generator, Only 2 models are produced. Rest are ignored. Some of the $ref are pointing to wrong model.

Here is example given below

openapi-generator version

4.0.0-beta

OpenAPI declaration file content or url

https://gist.github.com/vinodchitrali/c5cd3be1c8d6fb0d2fb6bcf6a530ad94

Command line used for generation

java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar  generate -i ./api/openapi.yaml   -g python -o /tmp/python/ --api-package api --model-package model --additional-properties projectName=python

Steps to reproduce

1. Copy the Yaml files from https://gist.github.com/vinodchitrali/c5cd3be1c8d6fb0d2fb6bcf6a530ad94
2. java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar generate -i ./api/openapi.yaml -g python -o /tmp/python/ --api-package api --model-package model --additional-properties projectName=python
3. Check files generated in /tmp/python/openapi_client/model/

Related issues/PRs

Suggest a fix

Start with the OpenAPI files in the linked Gist and reproduce the issue using the documented Java CLI command with the Python generator. Inspect how the generator resolves cross-file $ref entries and writes models under /tmp/python/openapi_client/model/. Done means all same-named schemas are handled without references pointing to the wrong model.