I would create a random open-source project, like a cloud FizzBuzz Enterprise Edition, and invite all these people to submit pull requests to this project instead. And accept all the pull requests so everyone get a t-shirt.
This doesn’t solve the fundamental issue that the spam causes maintainers to have to spend brain cycles dealing with it. This “solution” still requires you to mark the PR as “invalid” manually. All it does is close the issue, add a comment, and delete the PR branch (if exists). If you’re already marking the branch as invalid, you’ve already wasted your time.
Ah, so this is why people keep sending in meaningless PRs all of a sudden, going so far as to change properly spelled words to misspelled ones. I didn't quite get it.