Promote TPU nightly docker images to latest without verifying E2E Airflow tests

[SurbhiJainUSC]

Description

This PR updates the TPU nightly images pipeline to promote Docker images immediately after CI tests pass, bypassing the E2E Airflow tests.

Motivation / Context

Currently, we need a way to promote the Docker images without waiting for the E2E Airflow tests. This is being introduced as a temporary workaround until the dedicated promote_docker_image.yml workflow is fully stable.

Changes Made

• Added a new tag_docker_image job to .github/workflows/tpu_nightly_images_pipeline.yml.
• Configured the new job to run immediately upon the success of run_ci_tests.

FIXES: b/533456896

Tests

https://github.com/AI-Hypercomputer/maxtext/actions/runs/29959108887

Checklist

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• 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]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.