ci: add base_sha to codecov/codecov-action upload step

[chtruong814]

What does this PR do ?

ci: add base_sha to codecov/codecov-action upload step

This re-adds the intended change of #4445

However we had to revert its merge commit in this PR:
#4526

Github had an issue where it reverted another PR while merging 4445.

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[svcnvidia-nemo-ci]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/25141691029

[svcnvidia-nemo-ci]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/25152960782