Fix a regression introduced by #4625 for nightly runs

[balasaajay]

What does this PR do ?

Fix a regression introduced by #4625 where GitLab scheduled nightly and weekly pipelines stopped running real functional tests.

#4625 added LEGACY_SCOPE_ALIASES and applied it inside flatten_products, so recipes with scope: [nightly] get rewritten in memory to scope: "L2". The filter side (filter_by_scope) was left doing strict equality, so GitLab's --scope nightly (still the legacy value, per .gitlab/stages/04.functional-tests.yml) matched zero workloads. generate_jet_trigger_job.py then emitted the sleep 1 placeholder pipeline, which Slack reports as All 1 passed.

This PR adds _resolve_scope_alias and threads it through filter_by_scope so both sides of the comparison are in the same vocabulary. After the fix:

--scope nightly and --scope L2 both match the same number of nightly workloads. --scope weekly and --scope L3 both match the same number of weekly workloads. --scope mr-github / mr-github-slim continue to work for any external caller still on the legacy names. All other scopes (mr, mr-slim, unit-tests, *-broken, etc.) pass through unchanged.

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[balasaajay]

/ok to test 097b7ad

[balasaajay]

/ok to test 097b7ad

[balasaajay]

/ok to test 097b7ad

[balasaajay]

/ok to test a5cf918

[svcnvidia-nemo-ci]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/25714755059