I can generate 1,000 PRs today against an open source project using AI. I think you do care, you are only thinking about the happy path where someone uses a little AI to draft a well constructed PR.
There's a lot ways AI can be used to quickly overwhelm a project maintainer.
Then perhaps the way you contribute, review, and accept code is fundamentally wrong and needs to change with the times.
It may be that technologies like Github PRs and other VCS patterns are literally obsolete. We've done this before throughout many cycles of technology, and these are the questions we need to ask ourselves as engineers, not stick our heads in the sand and pretend it's 2019.
Before PR's existed we passed around code changes via email. Before containers we installed software on bare metal servers. And before search engines we used message boards. It's not unfathomable that the whole idea of how we contribute and collaborate changes as well. Actually that is likely going to be the /least/ shocking thing in the next few years if acceleration happens (i.e. The entire OS is an LLM that renders pixels, for example)