[Bugfix] `OPTDecoderLayer` does not return attentions when `gradient_checkpointing` and `training` is enabled.
# What does this PR do?

Reorder argument of OPTDecoderLayer.forward

Fixes #23366

_The documentation is not available anymore as the PR was closed or merged._<|||||>cc @younesbelkada @ArthurZucker 