Fix pyconfig for post train

[A9isha]

Description

Fix pyconfig to look for "models" after refactoring of sft.yml and rl.yml inside src/maxtext/configs/post_train

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Tests

Tested locally on v5p-8 with

python3 -m maxtext.trainers.post_train.sft.train_sft src/maxtext/configs/post_train/sft.yml run_name=check model_name=llama3.1-8b tokenizer_path=meta-llama/Llama-3.1-8B-Instruct hf_access_token=<token> load_parameters_path=/path/to/checkpoint steps=10

Checklist

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• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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