Fix: replace invalid Gemini model with gemini-1.0-pro

Author: N-Yashwitha

.github/workflows/presubmit.yml

@@ -32,4 +32,4 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           LLM_API_KEY: ${{ secrets.LLM_API_KEY }}
-          LLM_MODEL: "gemini-1.5-flash"
+          LLM_MODEL: "gemini-1.0-pro"