fix: Fix multi-node functional test phase sync

[chtruong814]

What does this PR do ?

fix: Fix multi-node functional test phase sync

The internal gb200 tests that resumed from a checkpoint were failing due to an update to nvrx. Codex doesn't think it's a regression in nvrx itself but exposed a problem in our test handling where multi-node tests would not properly wait for the other node to finish. In this case, the test would try to check for tensorboard logs of the first run too early.

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[balasaajay]

elegant approach. lgtm

[svcnvidia-nemo-ci]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/26285564016