chore(beep boop 🤖): Bump `MCORE_TAG=2d7c521...` (2025-01-06)
🚀 PR to bump `NVIDIA/Megatron-LM` in `Dockerfile.ci` to `MCORE_TAG=2d7c521de7c5878501cf7e366e7d8e13267c8eb6`.  

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

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