[BUG] Misleading metric type of LightevalTaskConfig

[wangtsuh]

Describe the bug

In the documentation and function LightevalTaskConfig, the metric argument has denoted list[str] as the type annotation. However, in the actual code, we can see that the expected type should be ListLike[Metric | Metrics]. The incorrect type annotation is misleading and causes users hard to know what list of string should be passed.

Version info

0.9.2

[NathanHB]

Hi ! Thanks for noticing, contributions for those kind of fix are welcomed if you want to open a PR :)