Wrong require in Cairo example

Within the example in https://github.com/crytic/building-secure-contracts/tree/master/not-so-smart-contracts/cairo/unchecked_from_address_in_l1_handler the require in `setOwnerOnL2()` should be:
```solidity
 require(OWNER == msg.sender, "not owner");
```
instead of
```solidity
 require(owner == msg.sender, "not owner");
```
