The assert_real_activation_start_race test used
set_decommission_space_info_override_for_test which creates capacity
infos via from_logical with take semantics (consumed on first access).
After the decommission capacity reservation model was introduced in
PR #6917, the capacity check reads actual physical disk space when
the override has already been consumed, causing the test to fail with
real disk values (~11TB required vs ~2TB available on a local Mac).
Switch to set_decommission_capacity_info_overrides_for_test which
uses a VecDeque (supports multiple snapshots for repeated access)
and provides properly formed DecommissionPoolCapacityInfo values
with matching erasure layout.