Fix typo in ts_model.py: change train_df.y to train_df[target_col]

[Programmer-RD-AI]

Why are these changes needed?

This PR addresses a typo in automl/timeseries/ts_model.py. The lines checking for zero values in the dataset incorrectly reference train_df.y instead of train_df[target_col]. This update ensures the correct column is referenced, improving the robustness of the parameter override logic for the Holt-Winters model.

Related issue number

Closes #1279

Checks

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• [x] I've added tests (if relevant) corresponding to the changes introduced in this PR.
• [x] I've made sure all auto checks have passed.