Set `use_cache` to `True` in `trocr` model
# What does this PR do?

- set `use_cache` to `True` for consistency with other `transformers` models
- With the PR https://github.com/huggingface/transformers/pull/18843 being merged, `trocr` became the last model in `transformers` that has `use_cache` set to `True`. 
- Except if there is any specific reason to let it to `False`, following #18843 , we think that it would be nice to set it to `True` for consistency with other models in `transformers` 
- All slow tests for `trocr` pass with this change

cc @stas00 @NielsRogge 

Thanks!
_The documentation is not available anymore as the PR was closed or merged._<|||||>Great works for me! Thanks @stas00 <|||||>Thanks for approving! Merging 