[Do NOT merge 🙏 ] Skip a particular exception in `test_sample_generate`
# What does this PR do?

A continuation of #17937 to fix a CI failure
```
            # sample
            probs = nn.functional.softmax(next_token_scores, dim=-1)
>           next_tokens = torch.multinomial(probs, num_samples=1).squeeze(1)
E           RuntimeError: probability tensor contains either `inf`, `nan` or element < 0
```

As @patrickvonplaten , when a broken generation happens due to all `-inf` scores along the vocab dimension, nothing we can do. This is likely to happen only with random models however.

Let's say goodbye to this flaky situation!
_The documentation is not available anymore as the PR was closed or merged._<|||||>Let's maybe put this PR on hold for 1,2 weeks to see if #18053 has solved the issue or not :-)<|||||>OK, thank you for taking time on this.