Start using py3.12 for TPU.

[vanbasten23]

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

Purpose

PyTorch/XLA (starting 07/14/2025) has dropped support for python 3.10 (the current python version that vLLM on TPU is using) and the next JAX version 0.7 will also drop support Python <3.11. This PR update the python version used in TPU to 3.12, consistent with the python version used for GPU.

Test Plan

CI

Test Result

TPU CI passed.

(Optional) Documentation Update

[github-actions]

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[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @vanbasten23.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[gemini-code-assist]

Code Review

This pull request updates the TPU Dockerfile and requirements to use Python 3.12. There is a potential issue with mismatched nightly dates between the base image and the installed packages. Please ensure the dates are aligned.

[gemini-code-assist]

The dates of these nightly packages (20250714) do not match the NIGHTLY_DATE (20250124) used for the base Docker image in docker/Dockerfile.tpu. Using mismatched dates can lead to runtime incompatibilities. Please align these dates to ensure a stable build.