update review model

Author: xlc

.github/workflows/polka-codes-review-pr.yml

@@ -40,7 +40,7 @@ jobs:
           config: .github/review.polkacodes.yml
         env:
           POLKA_API_PROVIDER: google-vertex
-          POLKA_MODEL: gemini-3-pro-preview
+          POLKA_MODEL: gemini-3.5-flash
           GITHUB_TOKEN: ${{ github.token }}
           GOOGLE_VERTEX_LOCATION: global
           GOOGLE_VERTEX_PROJECT: ${{ secrets.GOOGLE_VERTEX_PROJECT }}