Add explicit tie-breaker in pending balance deposits sort (#8772)

Co-authored-by: Enrico Del Fante <enrico.delfante@consensys.net>

Author: jtraglia

ethereum/spec/src/main/java/tech/pegasys/teku/spec/logic/versions/electra/forktransition/ElectraStateUpgrade.java

@@ -103,7 +103,9 @@ public BeaconStateElectra upgrade(final BeaconState preState) {
                   .boxed()
                   .sorted(
                       Comparator.comparing(
-                          index -> validators.get(index).getActivationEligibilityEpoch()))
+                              (Integer index) ->
+                                  validators.get(index).getActivationEligibilityEpoch())
+                          .thenComparing(index -> index))
                   .forEach(
                       index ->
                           beaconStateMutators.queueEntireBalanceAndResetValidator(state, index));