[StateAccumulatorV2] Re-enable on testnet (#18443)

## Description 

Same as #18444 but against the
release branch

## Test plan 

How did you test the new or updated feature?

---

## Release notes

Check each box that your changes affect. If none of the boxes relate to
your changes, release notes aren't required.

For each box you select, include information after the relevant heading
that describes the impact of your changes that a user might notice and
any actions they must take to implement updates.

- [ ] Protocol: 
- [ ] Nodes (Validators and Full nodes): 
- [ ] Indexer: 
- [ ] JSON-RPC: 
- [ ] GraphQL: 
- [ ] CLI: 
- [ ] Rust SDK:

crates/sui-core/src/authority/epoch_start_configuration.rs

@@ -61,7 +61,7 @@ impl EpochFlag {
 
     /// For situations in which there is no config available (e.g. setting up a downloaded snapshot).
     pub fn default_for_no_config() -> Vec<Self> {
-        Self::default_flags_impl(&Default::default(), false)
+        Self::default_flags_impl(&Default::default(), true)
     }
 
     fn default_flags_impl(

crates/sui-core/src/state_accumulator.rs

@@ -5,7 +5,7 @@ use itertools::Itertools;
 use mysten_metrics::monitored_scope;
 use prometheus::{register_int_gauge_with_registry, IntGauge, Registry};
 use serde::Serialize;
-use sui_protocol_config::ProtocolConfig;
+use sui_protocol_config::{Chain, ProtocolConfig};
 use sui_types::base_types::{ObjectID, ObjectRef, SequenceNumber, VersionNumber};
 use sui_types::committee::EpochId;
 use sui_types::digests::{ObjectDigest, TransactionDigest};
@@ -389,15 +389,13 @@ impl StateAccumulator {
         epoch_store: &Arc<AuthorityPerEpochStore>,
         metrics: Arc<StateAccumulatorMetrics>,
     ) -> Self {
-        if cfg!(msim) {
-            if epoch_store.state_accumulator_v2_enabled() {
-                return StateAccumulator::V2(StateAccumulatorV2::new(store, metrics));
-            } else {
-                return StateAccumulator::V1(StateAccumulatorV1::new(store, metrics));
-            }
+        if epoch_store.state_accumulator_v2_enabled()
+            && epoch_store.get_chain_identifier().chain() != Chain::Mainnet
+        {
+            StateAccumulator::V2(StateAccumulatorV2::new(store, metrics))
+        } else {
+            StateAccumulator::V1(StateAccumulatorV1::new(store, metrics))
         }
-
-        StateAccumulator::V1(StateAccumulatorV1::new(store, metrics))
     }
 
     pub fn new_for_tests(