Problem The test lookup_unwind_metrics.js fails on the enterprise-amazon-linux2023-arm64-roll-back-incremental-feature-flags build variant.

Root Cause The test asserts that the metrics.query.lookupUnwind serverStatus counters increment when a $lookup+$unwind pipeline runs in SBE. Those counters only increment when the SBE EqLookupUnwind IFR rollout flags (e.g. featureFlagSbeEqLookupUnwind) are enabled, because they control whether $lookup+$unwind is lowered into the SBE LU strategies. The roll-back-incremental-feature-flags variant disables the unreleased IFR flags (via disableUnreleasedIFRFlags). The test only guarded on SBE being enabled (checkSbeRestrictedOrFullyEnabled) and featureFlagGetExecutorDeferredEngineChoice; it never checked featureFlagSbeEqLookupUnwind. As a result, the pipeline fell back to classic, the counters never moved, and every assertion failed instead of the test skipping.

This is the same root cause as SERVER-129505, which fixed the analogous failure in engine_selection_deferred_executor.js.

Fix Add an early-exit guard that skips the test when featureFlagSbeEqLookupUnwind is disabled, mirroring the guard added in SERVER-129505.