I'm sorry if this makes me sound like a cranky old man but I find the idea of AI-generated PR description and reviews entirely misses the mark of what they're for. The PR description should contain the context that made a change necessary, which is something that can not be contained in the change itself and thus can't reliably be inferred from it. And if I request a PR review, I trust you , as my peer, to understand…
I find AI summaries to be useful when writing PR's as a starting point. Having it generate a bulleted list summarizing the changes is a good way to make sure you've covered your entire PR (and it's easy to trim down unnecessary things). You can add context as needed. I'd never trust an unrevised version though.
As is, getting in revised LLMs responses seems like it'll be Gen Alpha's "let me Google that for you" swipe. Except at least Googling means you still need to put in leg work.