Avoid GPU OOM for a TF Rag test
# What does this PR do?

After changing torch from `cu102` to `cu113`, the test `test_rag_token_generate_batch` on TF side causes GPU OOM.
This PR splits the batch into 2 batches to avoid this issue.

I can just run only 1 batch if you think it's better.
_The documentation is not available anymore as the PR was closed or merged._<|||||>Merged as the change is quite obvious and small + being approved by 1 maintainer.