fix test whisper with new max length
# What does this PR do?
Fixes pipeline test after `max_length` update 
@ydshieh 

Could you link the Hub PR that is related?
<|||||>_The documentation is not available anymore as the PR was closed or merged._<|||||>It seems the checkpoint involved is `openai/whisper-tiny.en` which is also used in other test methods. Could you confirm the other tests also pass after that Hub PR?<|||||>The `pytorch` tests all pass, 3 `TF` tests fails for now. 
Only the `config.max_length` was changed so should not have a lot of impact. 