fix(oas): retain response header references

[EdVinyard]

Motivation and Context

https://github.com/stoplightio/platform-internal/issues/17558

Description

like #246 and #248, but for response headers

How Has This Been Tested?

unit test added

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• [x] This PR's code follows as closely as possible the coding style/guidelines of this project.
• [ ] I have added error reporting and followed the error reporting guidelines.
• [ ] I have added event tracking and followed the event tracking guidelines.
• [ ] I have updated any relevant documentation accordingly to reflect this PR's changes.
• [x] I have added automated tests (unit/integration/e2e/other) to cover my changes.
• [x] All new and existing tests pass locally (excluding flaky CI tests).

[stoplight-bot]

:tada: This PR is included in version 5.12.1 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: