I'm surprised Iran doesn't block Github. There's plenty of political content on Github - it makes a half-decent blogging platform for the technically inclined.
You're right about censorship. However most Iranians have a VPN installed on their phone and rarely gets trouble for doing so and speak freely but anonymously. Iran gov is actually a democratie quite more liberal than most western people think. Yes, there is censorship, unfair courts cases, corruption, and repression. Still we can see this in most of the countries, often in harden terms. Should we speak about Assange ?
Github was available to Iranian up until two years ago. The general public is not that familiar with github (just like the rest of the world).
But it is very likely that if the government feel like it, they just go ahead and censor it.
Examples? I've never come across anything heavily political, aside from maybe "free software" advocacy, which I assume isn't something most governments find particularly threatening.
Not Iranian but a very famous repo is the 996 repo https://github.com/996icu/996.ICU (>250k stars) which advocates for Chinese Developers working a 996 schedule. Depending on where you look you can find a lot of political content on Github from all over the world.