fix: update Gemini model version in presubmit.yml (#3337)

The Presubmit.ai check was failing due to an outdated Gemini model version.
Updated LLM_MODEL from "gemini-1.5-flash" to "gemini-1.5-flash-latest" to fix the issue.

Author: prem-2006

.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-1.5-flash-latest"  # ✅ updated model version