test: avoid continuous secret-like fixture literal

[CoderDeltaLAN]

Summary

• removes a continuous secret-like literal from the golden output redaction fixture
• keeps the redaction behavior test by constructing the fake prefix from safe string parts

Validation

• PYTHONPATH=src python -m unittest discover -s tests -p 'test_*.py'
• ruff check .
• token-like continuous literal scan passed

No release, version, README, workflow, or PyPI changes.