Fix import error in ckpt_scripts

[RUEI4341]

Description

Resolve import error in src/MaxText/utils/ckpt_scripts/llama_mistral_mixtral_orbax_to_hf.py (line 51), introduced in PR#2601: "Consolidate legacy checkpoint scripts into folder".

If the change fixes a bug or a Github issue, please include a link, e.g.,:
FIXES: b/458573192

Tests

Will monitor the test in XLML

Checklist

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