[Gemini] Add Java GeminiModelHandler class - #39245

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: jwgmeligmeyling/spotbugs-github-action@v1.2. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Cache reservation failed: cache write denied: token has no writable scopes

Cache reservation failed: cache write denied: token has no writable scopes

Cache reservation failed: cache write denied: token has no writable scopes

Cache reservation failed: cache write denied: token has no writable scopes

Cache reservation failed: cache write denied: token has no writable scopes