[Consensus] enable consensus garbage collection for testnet (#21208)

## Description 

Enables the Consensus garbage collection for testnet. `gc_depth` is set
to `60` , which with the current round rate of 12-15 rounds/sec it
should allow the network to include blocks in a window of `4-5 seconds`.

## Test plan 

CI

---

## Release notes

Check each box that your changes affect. If none of the boxes relate to
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that describes the impact of your changes that a user might notice and
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- [x] Protocol: Enables consensus garbage collection for testnet
- [ ] Nodes (Validators and Full nodes): 
- [ ] gRPC:
- [ ] JSON-RPC: 
- [ ] GraphQL: 
- [ ] CLI: 
- [ ] Rust SDK:

crates/sui-protocol-config/src/lib.rs

@@ -217,6 +217,7 @@ const MAX_PROTOCOL_VERSION: u64 = 74;
 //             Enable all gas costs for load_nitro_attestation.
 //             Enable zstd compression for consensus tonic network in mainnet.
 //             Enable the new commit rule for devnet.
+//             Enable consensus garbage collection for testnet.
 
 #[derive(Copy, Clone, Debug, Hash, Serialize, Deserialize, PartialEq, Eq, PartialOrd, Ord)]
 pub struct ProtocolVersion(u64);
@@ -3245,6 +3246,12 @@ impl ProtocolConfig {
                     if chain != Chain::Mainnet && chain != Chain::Testnet {
                         cfg.feature_flags.consensus_linearize_subdag_v2 = true;
                     }
+
+                    if chain != Chain::Mainnet {
+                        // Assuming a round rate of max 15/sec, then using a gc depth of 60 allow blocks within a window of ~4 seconds
+                        // to be included before be considered garbage collected.
+                        cfg.consensus_gc_depth = Some(60);
+                    }
                 }
                 // Use this template when making changes:
                 //

crates/sui-protocol-config/src/snapshots/sui_protocol_config__test__Testnet_version_74.snap

@@ -348,6 +348,7 @@ max_soft_bundle_size: 5
 bridge_should_try_to_finalize_committee: true
 max_accumulated_txn_cost_per_object_in_mysticeti_commit: 37000000
 max_accumulated_randomness_txn_cost_per_object_in_mysticeti_commit: 7400000
+consensus_gc_depth: 60
 gas_budget_based_txn_cost_cap_factor: 400000
 gas_budget_based_txn_cost_absolute_cap_commit_count: 50
 sip_45_consensus_amplification_threshold: 5