Add trust_remote_code=True to load_datasets() for math and legalbench

[yifanmai]

This is required to avoid a breakage in the future:

FutureWarning: The repository for nguha/legalbench contains custom code which must be executed to correctly load the dataset. You can inspect the repository content at https://hf.co/datasets/nguha/legalbench
You can avoid this message in future by passing the argument `trust_remote_code=True`.
Passing `trust_remote_code=True` will be mandatory to load this dataset from the next major release of `datasets`.

[neelguha]

lgtm!