cp: build: widen flashinfer-python pin to <0.7.0 (#4700) into dev

[chtruong814]

What does this PR do ?

cp: build: widen flashinfer-python pin to <0.7.0 (#4700) into dev

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[chtruong814]

/ok to test 1f70419

[svcnvidia-nemo-ci]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/25754804259