The AAAA record for IPv6 might be using some sort of URL Redirect service. It needs to point directly to your nginx server to work properly. You need to ask Hostinger.
The IPv4 request reaches your nginx and gives the expected 404 response to this test. But, you can see IPv6 reaches a LiteSpeed server on platform:hostinger. While it gives a 404 response it won't be able to respond properly to an actual request started by Certbot.
curl -I4 http://webclass.in/.well-known/acme-challenge/Test404
HTTP/1.1 404 Not Found
Server: nginx/1.21.4
curl -I6 http://webclass.in/.well-known/acme-challenge/Test404
HTTP/1.1 404 Not Found
server: LiteSpeed
platform: hostinger