ci(ai): Only run mock responses check on AI PRs

[dlarocque]

When the check-version job in the .github/workflows/check-vertexai-responses.yml workflow fails, the job comments a warning on all PRs, even if they are unrelated to Firebase AI Logic. This is distracting for SDK developers who have no control over the version of the Firebase AI mock responses. I think this job should only add a comment to PRs that make changes to packages/ai.

[changeset-bot]

⚠️ No Changeset found

Latest commit: e648573

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[google-oss-bot]

Size Report ¹

Affected Products

No changes between base commit (22e0a1a) and merge commit (3b30d89).

Test Logs

• Base (22e0a1a): https://github.com/firebase/firebase-js-sdk/actions/runs/18658284611
• Merge (3b30d89): https://github.com/firebase/firebase-js-sdk/actions/runs/18687146627

1. https://storage.googleapis.com/firebase-sdk-metric-reports/ARMdwC8V30.html

[google-oss-bot]

Size Analysis Report ¹

Affected Products

No changes between base commit (22e0a1a) and merge commit (3b30d89).

Test Logs

• Base (22e0a1a): https://github.com/firebase/firebase-js-sdk/actions/runs/18658284611
• Merge (3b30d89): https://github.com/firebase/firebase-js-sdk/actions/runs/18687146627

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