fix: remove to_huggingface.py step from Gemma3-4B LoRA E2E test

[chiajunglien]

Description

Remove the final to_huggingface conversion step (Step 5) from the Gemma3-4B LoRA end-to-end test (tests/end_to_end/tpu/gemma3/4b/test_gemma3_lora.sh).

This step was not part of the original LoRA e2e flow; it was added by #4361.
Since then it has been breaking our DAG, so this PR reverts the script back to the LoRA-only flow.

DAG Error Log

Tests

https://efdb2a1d6c2c435b8b7de77690c286a9-dot-us-central1.composer.googleusercontent.com/dags/maxtext_e2e_tpu_post_training/grid?tab=logs&task_id=gemma3-4b.lora-gemma3-4b.lora-v5p-8.run_model.wait_for_workload_completion&dag_run_id=manual__2026-09-11T09%3A17%3A56%2B00%3A00

Checklist

Before submitting this PR, please make sure (put X in square brackets):

• I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run end-to-end tests tests and provided workload links above if applicable.
• 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.

[gemini-code-assist]

Code Review

This pull request introduces a temporary patch _patch_tunix_moe_weight_keys in maxtext_vllm_rollout.py to add missing MoE keys (specifically wo) to Tunix's zero-pad branch, preventing a ShapeMismatchError during rollout. It also removes the Hugging Face checkpoint conversion step from the Gemma3 LoRA end-to-end test. Feedback suggests simplifying the set operations in the patch function by directly using set operators on the existing set-like objects instead of performing redundant type conversions.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!