[ examples] fix loading jsonl with load dataset in run translation example (#26924)

* Renamed variable extension to builder_name

* If builder name is jsonl change to json to align with load_datasets

* Apply suggestions from code review
Co-authored-by: Quentin Lhoest <42851186+lhoestq@users.noreply.github.com>

---------
Co-authored-by: Quentin Lhoest <42851186+lhoestq@users.noreply.github.com>

examples/pytorch/translation/run_translation.py

@@ -374,8 +374,12 @@ def main():
         if data_args.test_file is not None:
             data_files["test"] = data_args.test_file
             extension = data_args.test_file.split(".")[-1]
+        if extension == "jsonl":
+            builder_name = "json"  # the "json" builder reads both .json and .jsonl files
+        else:
+            builder_name = extension  # e.g. "parquet"
         raw_datasets = load_dataset(
-            extension,
+            builder_name,
             data_files=data_files,
             cache_dir=model_args.cache_dir,
             token=model_args.token,