Don't encode lists as strings when using `Value("string")`
Following https://github.com/huggingface/datasets/pull/3456#event-5792250497 it looks like `datasets` can silently convert lists to strings using `str()`, instead of raising an error.

This PR fixes this and should fix the issue with WER showing low values if the input format is not right.
Should we close this PR? since the original issue has to do with metrics that have been moved to `evaludate` I think we can close this one _The documentation is not available anymore as the PR was closed or merged._