To be fair, Linux isn't developed on GitHub (it's developed on the Linux Kernel Mailing List and kernel.org) and most of the spammers knew that going into it. The PRs on that repo were mostly just people trolling any bystanders that took it seriously until the internet did what they do best and took the joke too far.

In this specific example they didn't waste anyone's time or resources because it was never being used or monitored in the first place.

Edit for more additional context: Linus (who created git in the first place) mentioned not liking centralized git servers so he's specifically said for multiple years that he never considered actually moving development over to something like GitHub