ci(autoupdate): simplify pull_request trigger to any PR to main

Per repo-owner preference, drop the explicit types list and use the
default pull_request event set, keeping only the base-branch filter
(branches: [main]).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/autoupdate.yml

@@ -18,7 +18,7 @@ on:
   push:
     branches: [main]
   pull_request:
-    types: [opened, reopened, ready_for_review]
+    branches: [main]
 
 permissions:
   contents: write