Checkpoint directory fix for E2E tests

[SurbhiJainUSC]

Description

• Fix base output directory for Gemma2 and Gemma3 E2E tests
• Fix import for llama_or_mistral_ckpt fixed in Fix checkpoint conversion script #2635

FIXES: b/447464486

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[RissyRan]

Thanks for the fix! Let's consolidate path into #2635?

[NuojCheng]

Thank you Surbhi for the fix!