skip Fuyu from test_generate

[nhamanasu]

What does this PR do?

skip Fuyu model from test_prompt_lookup_decoding_matches_greedy_search to fix tests_generate's failure.

Backgrounds

Recently, test_generate in CircleCI fails due to FuyuModelTest.
([reference] tests_generate - Failed)

The direct cause is RuntimeError: The size of tensor a (2) must match the size of tensor b (0) at non-singleton dimension 1, perhaps caused by eos_token_id should consist of positive integers, but is tensor([-1]). Your generation will not stop until the maximum length is reached. Depending on other flags, it may even crash.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

• generate: @zucchini-nlp

[Rocketknight1]

cc @ydshieh

[nhamanasu]

• The failure of tests_torch will be resolved in this PR: set supports_gradient_checkpointing = False in SwitchTransformer #35249

[zucchini-nlp]

Fuyu skips the other assisted decoding methods due to specific way inputs have to be handled, afaik. So I'll be ok with skipping it, if @ydshieh agrees

[ydshieh]

LGTM, thank you for the PR 🙏