Bump 3rdparty/Megatron-LM from f8d3e2e to f4fa7d6

Bumps [3rdparty/Megatron-LM](https://github.com/NVIDIA/Megatron-LM) from `f8d3e2e` to `f4fa7d6`.
- [Release notes](https://github.com/NVIDIA/Megatron-LM/releases)
- [Commits](NVIDIA/Megatron-LM@f8d3e2e...f4fa7d6)

---
updated-dependencies:
- dependency-name: 3rdparty/Megatron-LM
  dependency-version: f4fa7d6bb9d10873a58fa736cacd22e11db706d2
  dependency-type: direct:production
...

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Author: dependabot[bot]