Fix issues #13569, #6077, and #13080

[manish08k]

Description

This PR addresses the following issues:

• [Composer][airflow_db_cleanup] - All DAGs runs older than max_db_entry_age_in_days are deleted #13569 — Airflow DB cleanup
• google.api.Service config seems to require an audience to avoid JWT validation errors #6077 — Endpoints JWT audiences
• Provide guidance on creating a header for streaming_synthesize in streaming_tts_quickstart.py #13080 — Text-to-Speech streaming WAV

Changes

• Updated the Airflow database cleanup sample.
• Updated Endpoints JWT audience configuration.
• Updated the Text-to-Speech streaming WAV sample.

Testing

• Verified the changes against the current main branch.
• Ran git diff --check.

Related Issues

Fixes #13569
Fixes #6077
Fixes #13080

[gemini-code-assist]

Code Review

This pull request updates the Airflow DB cleanup workflow, adds commented-out configuration instructions for custom JWT audiences in the Bookstore gRPC endpoints, and updates the Text-to-Speech streaming quickstart snippet to write the audio stream into a playable WAV file. In airflow_db_cleanup.py, removing + [None] prevents rows with a NULL dag_id from being cleaned up. A suggestion was made to use a list comprehension that preserves None as None and only converts non-null values to strings.

[gemini-code-assist]

By removing + [None], any database rows with a NULL dag_id (which are common in tables like Log) will never be cleaned up. Furthermore, converting None to a string (str(None)) results in "None", which causes a useless query for a DAG literally named "None".

Using a list comprehension that preserves None as None and only converts non-null values to strings solves both issues: it correctly cleans up NULL dag_id rows when they exist, avoids querying for the literal string "None", and avoids running redundant None queries for tables that do not contain any NULL dag_ids.

Suggested change

	list_dags = [str(list(dag)[0]) for dag in dags]
	list_dags = [str(dag[0]) if dag[0] is not None else None for dag in dags]