`unexpected symbolic argument` for prove tests with two `uint` args

This test fails with `hevm: unexpected symbolic argument`:

```solidity
function proveSmth(uint x, uint y) public {}
```

This one doesn't :thinking:

```solidity
function proveSmth(uint x) public {}
```

Both run fine the debugger, it's just when running as a command line unit test that we run into issues....