[testnet] Fix minor bug in forge terraform
[testnet] Fix minor bug in forge terraform

This was preventing a non forge testnet from coming online because it assumed there was a index 0

aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core