It seems like there is a ready solution here, have an LLM review and filter pull requests from unknown sources before you read them. My understanding is there are semi-reliable ways to detect AI writing, maybe there is an analog for code. In any case, you can filter according to criteria you set. Analysis and bug-finding is where LLMs shine, much more than their ability to generate code.

I can understand wanting to minimize your interaction with LLMs, so this might not be an attractive solution. But it seems like a worthwhile feature to have on the platform level for people who would like to continue to accept pull requests without the frustration.