fix: Run pw_mcjax_benchmark_recipe on a smaller cluster

[RUEI4341]

Description

This change updates the DAG pw_mcjax_benchmark_recipe to use a smaller, v6e-8 cluster.

Checklist

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

• I have performed a self-review of my code.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run one-shot tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed.