Turns out that #175 was not enough to make Symfony happy:
```
Method "ArrayAccess::offsetGet()" might add "mixed" as a native return type declaration in the future. Do the same in implementation "FriendsOfBehat\SymfonyExtension\Mink\MinkParameters" now to avoid errors or add an explicit @return annotation to suppress this message.
```
Return type of FriendsOfBehat\SymfonyExtension\Mink\MinkParameters::offsetGet($offset) should either be compatible with ArrayAccess::offsetGet(mixed $offset): mixed, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice
