To hell with writing a test for you. That’s what you say to someone who gets paid by you. If the project doesn’t want the fix. That’s their issue, not the reporter’s.
One way is for the PR maker to signal their own attention to detail/effort/commitment by jumping through the (quite reasonable) hoop of writing a test.
Is this extra effort? Yes. But if your motivation in opening the PR in the first place is genuinely to improve the world, then do the slightly harder thing that actually improves the world given the constraints on maintainer attention it operates under, not the thing that is slightly easier for you but leaves your contribution indistinguishable from the sea of slop out there.