fix transfer OCI index

[mandelsoft]

Description

The transfer of OCI indix manifests accidently rewrites the manifest, even if it has not been changed during a transfer step.

What type of PR is this? (check all applicable)

• [ ] 🍕 Feature
• [ ] 🐛 Bug Fix
• [ ] 📝 Documentation Update
• [ ] 🎨 Style
• [ ] 🧑‍💻 Code Refactor
• [ ] 🔥 Performance Improvements
• [ ] ✅ Test
• [ ] 🤖 Build
• [ ] 🔁 CI
• [ ] 📦 Chore (Release)
• [ ] ⏩ Revert

Related Tickets & Documents

• Related Issue # (issue)
• Closes # (issue)
• Fixes # (issue)

  Remove if not applicable

Screenshots

Added tests?

• [ ] 👍 yes
• [ ] 🙅 no, because they aren't needed
• [ ] 🙋 no, because I need help
• [ ] Separate ticket for tests # (issue/pr)

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

Added to documentation?

• [ ] 📜 README.md
• [ ] 🙅 no documentation needed

Checklist:

• [ ] My code follows the style guidelines of this project
• [ ] I have performed a self-review of my code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes
• [ ] Any dependent changes have been merged and published in downstream modules

[ccwienk]

/lgtm - successfully tested replication of ImageIndex-OCI-Artefact