why nginx load balancer over port 80 loads nginx welcome page?

Question

I am trying to make a load balancer using nginx upstream. My nginx upstream config is as below:

upstream my_upstream {
    server test.mydomain.com:80;
}
server {
    server_name upstream.mydomain.com;
    location / {
            proxy_pass http://my_upstream;
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection 'upgrade';
            proxy_set_header Host $host;
            proxy_set_header X-Forwarded-For $remote_addr;
            proxy_cache_bypass $http_upgrade;
            proxy_buffering off;
            proxy_request_buffering off;

            add_header Last-Modified $date_gmt;
            if_modified_since off;
            expires off;
            etag off;
    }


    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/upstream.mydomain.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/upstream.mydomain.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}
server {
    if ($host = upstream.mydomain.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot
    server_name upstream.mydomain.com;
    listen 80;
    return 404; # managed by Certbot
}

And my node server nginx config is like this:

server {
    server_name test.mydomain.com;

    location / {
            proxy_pass http://localhost:9000;
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection 'upgrade';
            proxy_set_header Host $host;
            proxy_set_header X-Forwarded-For $remote_addr;
            proxy_cache_bypass $http_upgrade;
            proxy_buffering off;
            proxy_request_buffering off;

            add_header Last-Modified $date_gmt;
            if_modified_since off;
            expires off;
            etag off;
    }
}

but when I open https://upstream.mydomain.com it shows nginx welcome page instead of my website homepage. how can I fix it?