fix: restore mainnet prover agents to 4 replicas (#22305)

Author: AztecBot

spartan/environments/mainnet.env

@@ -11,7 +11,7 @@ VERIFY_CONTRACTS=false
 DEPLOY_INTERNAL_BOOTNODE=false
 VALIDATOR_REPLICAS=0
 RPC_REPLICAS=1
-PROVER_REPLICAS=0
+PROVER_REPLICAS=4
 
 FISHERMAN_REPLICAS=1
 FISHERMAN_MNEMONIC_START_INDEX=1