The best option to do is contact BHARTI Airtel Ltd. which the IP links back too.
It happens occasionally with Comcast in the US blocking sites for security reasons
It sounds like this issue might be similar to the one mentioned in this post where Cloudflare’s IPs were being blocked because another domain using Cloudflare contained “illegal” content.
If that is the case there’s nothing you can really do except for changing plans which I think will result in your site being assigned different Cloudflare IPs. Though someone will have to confirm that
The connection from CloudFlare → Upstream is configured over HTTP (instead of HTTPS) and CloudFlare’s ISP (Airtel in this scenario) is the one actually doing the block, so to the user it appears with a green padlock.
If you switch from HTTP to HTTPS on the origin connection, this gets fixed because Airtel can’t MITM TLS without CloudFlare noticing. You’ll need to enable HTTPS on the GitHub end, but that is also fairly straightforward: Securing your GitHub Pages site with HTTPS - GitHub Docs