Adding lm-eval 0.3.0 as an install req in llama2 (#2394)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/2394

Adding install reqs for enabling model evaluation in llama2.

The versions are intentional due to conflicts with ET install reqs

pip install datasets==2.14.0
pip install lm-eval==0.3.0

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Reviewed By: jerryzh168

Differential Revision: D54839623

fbshipit-source-id: 0ccf588172a707de6c16c693179946b64c428465