Bump 3rdparty/Megatron-LM from 2da43ef to 65720c8

Bumps [3rdparty/Megatron-LM](https://github.com/NVIDIA/Megatron-LM) from `2da43ef` to `65720c8`.
- [Release notes](https://github.com/NVIDIA/Megatron-LM/releases)
- [Commits](NVIDIA/Megatron-LM@2da43ef...65720c8)

---
updated-dependencies:
- dependency-name: 3rdparty/Megatron-LM
  dependency-type: direct:production
...

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