[Arbitrary Txs] Array encoding issue

[jakubcolony]

Steps to reproduce

Reproducing this is kinda cumbersome, with the easiest way being deploying our own test contract.

Follow steps 1-5 from #3966, but replace the contents of TestContract.sol with the following:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract TestContract {
    function testFunction(uint256[] memory numbers) public {}
}

Once the contract is deployed, add a transaction with its address and the following JSON ABI:

[
  {
    "inputs": [
      {
        "internalType": "uint256[]",
        "name": "numbers",
        "type": "uint256[]"
      }
    ],
    "name": "testFunction",
    "outputs": [],
    "stateMutability": "nonpayable",
    "type": "function"
  }
]

Select the testFunction and enter any value that is a valid array of integers ([], [1, 2, 3], and so on).

Submit the form.

Expected behaviour

The transaction goes through successfully.

Actual behaviour

The saga throws an error and silently fails. This is because ethers' encodeFunctionData is expecting a first-class array but it is passed the string representation instead.