fix: bump mlm to fix NVBug 6432008

[yuki-97]

cherry-pick NVIDIA/Megatron-LM#5715 in mlm based on current mlm commit.

[copy-pr-bot]

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[github-actions]

✅ Submodule Fast-Forward Check Results

Check based on commit: a7e7afb (PR #3265 from yukih/bump-mbridge-mlm)

✅ Submodules that are properly updated:

Megatron-Bridge: ✅ PR branch is ahead of r0.7.0 branch (fast-forward)

All submodule changes look good! ✨

[qiaochuz-nv]

Cherry-pick and verification completed.

Cherry-pick:
- PR: NVIDIA-NeMo/RL #3265, targets r0.7.0
- Created isolated worktree:
  /home/qiaochuz/nemo/RL_bv_6432008
- Branch: qiaochuz/nvbug-6432008-mlm
- Cherry-pick commit: eeb23dbab1fa6feb6480de1f72641c2f9afbdd6c
- Worktree is clean.

PR #3265 updates Megatron-Bridge to commit 151168f..., whose nested Megatron-LM is:
7b8495881dee1689db9d5ed636d8b6b48eacf260
- Includes Megatron-LM #5715.
- Verified transfer_bookkeeping_to_gpu() now uses:
  python
  self.gpu_view.buf.copy(self._cpu_bookkeeping_buf, non_blocking=False)


Fresh verification:
- Base container: nemo-rl-nightly-20260717.sqsh
- The released nightly itself remains unpatched, so the run used that nightly base with only the cherry-picked Megatron-LM source mounted over:
  /opt/nemo-rl/3rdparty/Megatron-Bridge-workspace/Megatron-Bridge/3rdparty/Megatron-LM
- Run ID: 20260717T171327Z-f03c198e
- SLURM job: 5659049
- Node: eos0044
- SLURM: COMPLETED 0:0, elapsed 00:03:58

Result:
text
test_grpo_megatron_generation: passed
effective exit code: 0
duration: 158s
metric: max(train/gen_kl_error) = 0.0004232723731547594 < 0.01

pass

[qiaochuz-nv]

run pass.

[terrykong]

/ok to test a7e7afb

[yuki-97]

/ok to test 84d4921

[github-actions]

✅ Submodule Fast-Forward Check Results

Check based on commit: 84d4921 (PR #3265 from yukih/bump-mbridge-mlm)

✅ Submodules that are properly updated:

Megatron-Bridge: ✅ PR branch is ahead of r0.7.0 branch (fast-forward)

All submodule changes look good! ✨