[BazelBot] Bump Gemini to 3.1 Pro

3.0 is deprecated and is now returning 404 on Vertex AI endpoints.

Author: boomanaiden154

google-bazel-bot/bazel-bot/bazel_agent.py

@@ -32,7 +32,7 @@
 USER_ID = "default_user"
 APP_NAME = "bazel_fixer"
 
-MODEL = "gemini-3-pro-preview"
+MODEL = "gemini-3.1-pro-preview"
 
 CODE_FIXER_PROMPT = """
 ## Context