Fix OS err

[muellerzr]

What does this PR do?

There's an issue with #35580 where if we have too many GPUs, we hit race conditions while trying to do the os.rename/move. Since we only need this once per node, really it just needs to happen under args.should_save (since that will make it happen only once per node or per instance as a whole if not doing save-on-each-node).

This PR fixes this race condition.

I tested it on the cluster on 8 GPUs, which replicated the issue

Fixes #36076

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@SunMarc

[SunMarc]

Looks fine to me. Let's wait a bit to see if this fixes the issue you linked !

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