Fix `SpeechT5` doctests
# What does this PR do?

PR #24434 changes `np.random.uniform(0, 1)` to `torch.rand([])`. In the forward method of `SpeechT5ForSpeechToSpeech` and `SpeechT5ForTextToSpeech`, the line `dropout_probability = torch.rand([])` is executed no matter if we are in training/inference mode. So the new change in #24434 will change the random sequences even we set a seed in the beginning of `generate`, and we get different outputs now.

Hence this PR updates the expected values for doctest.

**However, I believe we should only call `dropout_probability = torch.rand([])` under the condition of being in training mode.**
WDYT?
_The documentation is not available anymore as the PR was closed or merged._<|||||>Yes, that would be a better fix I agree.<|||||>Thanks, I will follow the same fix in #24486 instead.