Avoid flaky generation sampling tests
# What does this PR do?

Avoid the CI failure
```bash
tests/models/switch_transformers/test_modeling_switch_transformers.py::SwitchTransformersModelTest::test_beam_sample_generate_dict_output
(line 3099)  RuntimeError: probability tensor contains either inf, nan or element < 0
```

For 
```bash
tests/models/marian/test_modeling_marian.py::MarianStandaloneDecoderModelTest::test_sample_generate
(line 2482)  RuntimeError: probability tensor contains either inf, nan or element < 0
```
it's not clear what I can change in https://github.com/huggingface/transformers/blob/6c62cfb2eff095c181481d8ae86c7f836b65d2d7/tests/generation/test_utils.py#L108-L155

I changed to `logits_warper_kwargs, logits_warper = self._get_warper_and_kwargs(num_beams=2)` despite this is not beam sampling test.
_The documentation is not available anymore as the PR was closed or merged._