PR board: Stop touching archived items (#59428)

The GitHub workflow was sometimes failing when someone edited the
already-merged PR that had been archived on the board because archived
items can't have their fields changed. The project board fields don't
need to be updated when the PR is already merged or closed.

Release Notes:

- N/A

script/github-community-pr-board.py

@@ -784,6 +784,10 @@ if __name__ == "__main__":
         print(f"Skipping draft PR #{pr['number']}")
         sys.exit(0)
 
+    if pr.get("state") != "open":
+        print(f"Skipping PR #{pr['number']} (state: {pr.get('state')})")
+        sys.exit(0)
+
     print(f"Processing PR #{pr['number']}: action={action}")
 
     if action in ("labeled", "unlabeled"):