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.

[gemini-code-assist]

The comment on line 21 states that this is a Docker-based sample, testing only against the Python version specified in the Dockerfile (3.11). However, the ignored_versions list only ignores 3.8, 3.9, and 3.10, which means tests will still run on 3.12, 3.13, and 3.14. To align with the comment and avoid redundant test runs on other Python versions, please ignore all versions except 3.11.

Suggested change

	"ignored_versions": ["3.8", "3.9", "3.10"],
	"ignored_versions": ["3.8", "3.9", "3.10", "3.12", "3.13", "3.14"],

References

1. When upgrading test dependencies that require a minimum Python version, ensure that test configurations (e.g., ignored_versions in noxfile_config.py) are updated to ignore incompatible Python versions.