fix: Fix incorrect issuer balance check in withdrawal test

[mdqst]

I noticed a mistake in the test "Withdraw to all issuers and owner." The current code uses issuer1Signer to check the balance of issuer2, which is logically incorrect.
This causes the test to verify the balance of issuer1 instead of issuer2, leading to inaccurate results.

i've corrected the signer to ensure the proper balance is checked.

Here's the fix:

const issuer2BalanceAfterWithdraw = await payment.connect(issuer2Signer).getMyBalance();