fix: write ModelTrainer train script with LF line endings

sagemaker-train/src/sagemaker/train/model_trainer.py

@@ -1061,7 +1061,7 @@ def _prepare_train_script(
             execute_driver=execute_driver,
         )
 
-        with open(os.path.join(tmp_dir.name, TRAIN_SCRIPT), "w") as f:
+        with open(os.path.join(tmp_dir.name, TRAIN_SCRIPT), "w", newline="\n") as f:
             f.write(train_script)
 
     @classmethod

sagemaker-train/tests/unit/train/test_model_trainer.py

@@ -559,9 +559,10 @@ def test_train_with_distributed_config(
         )
 
         assert os.path.exists(expected_train_script_path)
-        with open(expected_train_script_path, "r") as f:
+        with open(expected_train_script_path, "rb") as f:
             train_script_content = f.read()
-            assert test_case["expected_template"] in train_script_content
+            assert test_case["expected_template"] in train_script_content.decode("utf-8")
+            assert b"\r\n" not in train_script_content
 
         assert os.path.exists(expected_runner_json_path)
         with open(expected_runner_json_path, "r") as f:
@@ -1529,4 +1530,4 @@ def test_llmft_recipe_missing_training_image_error(modules_session):
             )
 
         # Clean up the temporary file
-        os.unlink(recipe.name)
+        os.unlink(recipe.name)