As of January 2023, raw.githubusercontent.com domain is blocked by Jio and possibly other ISPs in India. This likely is due to a wise government or court order. There is a substantial Hacker News thread discussing this issue, but the situation has been the same now, for more than a couple of months.

The block seems to be at the DNS level and I had sucess with using Google's Public DNS server.

To change the DNS server I updated the DNS servers setting in the Jio broadband router under Network > LAN > DNS servers. Change the option to select Use Below and enter Google's primary and secondary DNS servers viz. 8.8.8.8 and 8.8.4.4.. The DNS Servers setting seems to get reset to Use DNS Proxy, every time I reboot the router. So, finally I had to set the custom DNS directly on my PC.

On my Redmi phone, there is no way to set a custom DNS as the setting has been removed by Xiaomi. The easiest way to overcome this was to use 1.1.1.1 + Warp from Cloudflare. This provides a VPN configuration that uses Cloudflare's free DNS resolver at 1.1.1.1.

Sometimes the DNS server change didn't seem to work on my desktop. In this case, I got unblocked by using the Tor Browser. This doesn't help with other apps that make a request to raw.githubusercontent.com. I ran into this problem again when installing Doom Emacs which unfortunately needed to download some files from the cursed github domain. After some Googling, I ended up using ProxyChains to make the Doom Emacs install command to use the local tor connection.

sudo service tor start
sudo apt install proxychains
proxychains ~/.config/emacs/bin/doom install

Yay! I don't need to buy a VPN now, just because I cheaped out choosing Jio.

Update: As of 5 October, 2023, I am still unable to access content from raw.githubusercontent.com when using Jio Broadband unless I use one of the above techniques.