`run_system_cached` does not allow usage of systems which return `Result`

Bevy 0.16

```rs
commands.run_system_cached(my_system);
```

```rs
pub fn my_system(
    // SNIP
) -> Result {
```

This causes an error on `run_system_cached`, because `my_system` is now a system with output type `Result` instead of `()`.

This is caused by the 0.16 system `Result` and `?` rework.