Prevent concurrent modification of battery history in tests

Bug: 270159981
Test: atest FrameworksServicesTests:BatteryStatsTests
Change-Id: I8a031a64a1d7d0f3e9c3abafdae6cd722f639408
diff --git a/services/tests/servicestests/src/com/android/server/power/stats/MockBatteryStatsImpl.java b/services/tests/servicestests/src/com/android/server/power/stats/MockBatteryStatsImpl.java
index f803355..d78ab867 100644
--- a/services/tests/servicestests/src/com/android/server/power/stats/MockBatteryStatsImpl.java
+++ b/services/tests/servicestests/src/com/android/server/power/stats/MockBatteryStatsImpl.java
@@ -231,6 +231,10 @@
         setExternalStatsSyncLocked(mExternalStatsSync);
     }
 
+    @Override
+    public void writeSyncLocked() {
+    }
+
     public static class DummyExternalStatsSync implements ExternalStatsSync {
         public int flags = 0;