Allow running conversion after closing a previous PR.

convert.py

@@ -232,7 +232,7 @@ def previous_pr(api: "HfApi", model_id: str, pr_title: str, revision=Optional[st
     except Exception:
         return None
     for discussion in discussions:
-        if discussion.status in {"open", "closed"} and discussion.is_pull_request and discussion.title == pr_title:
+        if discussion.status == "open" and discussion.is_pull_request and discussion.title == pr_title:
             commits = api.list_repo_commits(model_id, revision=discussion.git_reference)
 
             if revision_commit == commits[1].commit_id: