De-flake CpuPowerStatsCollectorTest#isolatedUidReuse

The root cause of the flakiness is the implementation of
PowerStatsCollector.forceSchedule(), which posts the next
collection event at the front of the event queue, which
messes with the order of events as expected by the test.

Bug: 337087734
Test: atest --rerun-until-failure 500 PowerStatsTests:CpuPowerStatsCollectorTest#isolatedUidReuse
Flag: com.android.server.power.optimization.streamlined_battery_stats
Change-Id: I02b0a7d9a8d8e4ab09c13fe143a484bf42f1b344