Chore - Integration test for increasing signer set from x to x+1, without threshold change

1. Description

We need a new integration test which simulates growing the signer set from x to x+1 to ensure that this process works correctly. This test does not need to handle threshold changes, which is currently not supported.

2. Why It's Necessary

This is to help ensure the process of growing the signer set in preparation for adding a new signer.