chore(beep boop 🤖): Bump `MCORE_TAG=81fee9b...` (2024-11-21)
🚀 PR to bump `NVIDIA/Megatron-LM` in `Dockerfile.ci` to `MCORE_TAG=81fee9b0047fb3ac6001b5e71e4df89fc01b2a1c`.  

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

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