chore(dataflow/gemma): update dependencies and format code

[XrossFox]

Description

• Update tensorflow base image to 2.20.0-gpu and beam sdk to 3.11/2.74.0
• Update apache_beam, keras, keras_nlp, and protobuf dependencies
• Update test dependencies including google-cloud-aiplatform, storage, and pytest
• Format custom_model_gemma.py and e2e_test.py
• Update ignored python versions in noxfile_config.py

Fixes b/521868825

Checklist

Testing

• I have tested this change on a live environment and verified it works as intended.

Compliance & Style

• I have followed the Sample Guidelines.
• The README is updated with all relevant information (if applicable).
• If this PR adds a new sample directory: I updated the CODEOWNERS file.

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Post-Approval Actions

• Please merge this PR for me once it is approved

[gemini-code-assist]

Code Review

This pull request updates the Gemma Dataflow sample by changing the Python SDK base image from version 3.14 to 3.11, upgrading TensorFlow to 2.20.0, and updating Apache Beam to 2.74.0. It also upgrades several runtime and test dependencies and applies code formatting across multiple files. Feedback on the changes suggests updating noxfile_config.py to ignore Python versions 3.12, 3.13, and 3.14 to align with the target Python 3.11 environment and prevent redundant test runs.

[XrossFox]

/gemini review

[gemini-code-assist]

Code Review

This pull request updates the project to Python 3.11, bumps dependency versions in the Dockerfile and requirements files, and modifies the end-to-end test configuration. The reviewer identified critical issues where several specified Docker image and PyPI package versions do not exist, which will cause build and installation failures. Additionally, changing the GCS test bucket to a hardcoded personal bucket in the end-to-end tests will break the CI/CD pipeline.

[XrossFox]

I have finally managed to get this sample running, it is working as expected:

(working on linting issues)