Add missing changelog

[daymxn]

Adds the changelog entry for #6652

[github-actions]

Release note changes

The following release notes were modified. Please ensure they look correct.

Release Notes

firebase-vertexai

### {{firebase_vertexai}} version 16.1.0 {: #vertex-ai_v16-1-0}

- [changed] Internal improvements to correctly handle empty model responses.

[github-actions]

Vertex AI Mock Responses Check ⚠️

A newer major version of the mock responses for Vertex AI unit tests is available. update_responses.sh should be updated to clone the latest version of the responses: v6.1

[google-oss-bot]

Coverage Report ¹

Affected Products

No changes between base commit (31e0d06) and merge commit (c61b38f).

Test Logs

• Merge (c61b38f): https://github.com/firebase/firebase-android-sdk/actions/runs/13040255205

1. https://storage.googleapis.com/firebase-sdk-metric-reports/JJ0jc1AZOh.html

[google-oss-bot]

Size Report ¹

Affected Products

No changes between base commit (31e0d06) and merge commit (c61b38f).

Test Logs

• Base (31e0d06): https://github.com/firebase/firebase-android-sdk/actions/runs/13039810991
• Merge (c61b38f): https://github.com/firebase/firebase-android-sdk/actions/runs/13040255205

1. https://storage.googleapis.com/firebase-sdk-metric-reports/I5HBSj6xg7.html