A year ago I changed my CONTRIBUTING document to say that I don't accept pull-requests on my very modest open source project (a special purpose DNS server)

I like coding, but am not fond of reviewing other people's code.

Also, the few PRs I received weren't up to snuff: for example, they included code changes but not tests. If they included tests, they weren't comprehensive. And they never included documentation changes.

I think it's fine. Open source does not mean at all that it has to be open development. Doesn't mean it cannot be, of course.