Receive duplicate response header `Connection: upgrade`

I want to simulate an HTTP 101 status code as follows.

# nginx.conf

worker_processes  1;
error_log logs/error.log debug;

events {
    worker_connections 1024;
}

http {
    lua_code_cache on;
    lua_package_path 'assets/?.lua;;';

    server {
        server_name www.example.com;
        listen 80;

        default_type text/html;

        access_log logs/access.log combined;

        location / {
            header_filter_by_lua_block {
                ngx.status = ngx.HTTP_SWITCHING_PROTOCOLS
                ngx.header["Connection"] = 'upgrade'
                ngx.header["Upgrade"] = 'foo/1, webscocket,bar/2'
                return ngx.exit(ngx.HTTP_OK)
            }
        }

    }
}

But got duplicate Connection: upgrade header:

root@73c270625dcb:/# curl -i localhost
HTTP/1.1 101 Switching Protocols
Server: openresty/1.25.3.2
Date: Fri, 07 Feb 2025 12:11:28 GMT
Content-Length: 0
Connection: upgrade
Connection: upgrade
Upgrade: foo/1, webscocket,bar/2

curl: (52) Empty reply from server

Start with the nginx.conf reproduction and the header_filter_by_lua_block shown in the issue, then run the curl request to inspect the HTTP/1.1 response. Trace how the 101 response and ngx.header["Connection"] are handled; done means the response contains only one Connection: upgrade header while retaining the Upgrade header.