test(e2e): upgrade model from gemini-1.5-flash to gemini-2.5-flash

[dlarocque]

Upgrade the model from gemini-1.5-flash to gemini-2.5-flash, since 1.5-flash is deprecated, and causes the e2e tests to fail.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 585c4d5

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[google-oss-bot]

Size Report ¹

Affected Products

No changes between base commit (0bb2fe6) and merge commit (fe24359).

Test Logs

• Base (0bb2fe6): https://github.com/firebase/firebase-js-sdk/actions/runs/18106196419
• Merge (fe24359): https://github.com/firebase/firebase-js-sdk/actions/runs/18106925792

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

[google-oss-bot]

Size Analysis Report ¹

Affected Products

No changes between base commit (0bb2fe6) and merge commit (fe24359).

Test Logs

• Base (0bb2fe6): https://github.com/firebase/firebase-js-sdk/actions/runs/18106196419
• Merge (fe24359): https://github.com/firebase/firebase-js-sdk/actions/runs/18106925792

1. https://storage.googleapis.com/firebase-sdk-metric-reports/x3CPauLiS7.html