chore(beep boop 🤖): Bump `MCORE_TAG=4dc8977...` (2025-01-08)
🚀 PR to bump `NVIDIA/Megatron-LM` in `Dockerfile.ci` to `MCORE_TAG=4dc8977167d71f86bdec47a60a98e85c4cfa0031`.  

📝 Please remember the following to-do's before merge: 
- [ ] Verify the presubmit CI  

🙏 Please merge this PR only if the CI workflow completed successfully.