chore: reduce gemini review spam (#3712)

Author: coryan

.gemini/config.yaml

@@ -23,6 +23,7 @@ code_review:
   max_review_comments: -1
   pull_request_opened:
     help: false
-    summary: true
+    # This is spammy, it repeats things we already know.
+    summary: false
     code_review: true
     include_drafts: true