Update the tpu dependency installation command

[tengyifei]

Description

Since libtpu is switching Python package registries, we need to include both registries during the transition. https://github.com/pytorch/xla/blob/master/README.md is already updated but we need to update these hardcoded commands here as well.

Tests

Verified things in a test composer instance:

bash scripts/upload-tests.sh gs://us-central1-piz-a9563b85-bucket/dags
# Check results in http://shortn/_xCUuG2UI33

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.

[ManfeiBai]

Thanks, let's megre after we saw green run in http://shortn/_xCUuG2UI33