 fix: verify jsonlines file in run_translation (#14660)
# What does this PR do?

Fixes #14660 

The documentation and the code everywhere mention jsonlines file except in the actual code where the verification was for json file instead.

## Before submitting
- [x] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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      Pull Request section?
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      [documentation guidelines](https://github.com/huggingface/transformers/tree/master/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/master/docs#writing-source-documentation).
- [x] Did you write any new necessary tests?


## Who can review?

Examples:

- maintained examples (not research project or legacy): @sgugger, @patil-suraj



Thanks for your PR! You should accept both extensions as there are many jsonline files that actually have the .json extension.<|||||>Thanks @sgugger , it is fixed now