It’s relatively easy to write a failing test and it massively cuts down the work related to moderating issues. Also, reduces the danger of github issues turning into a support forum.
If this results in the project being easier to maintain and being maintained longer, then I’m fine with this.
In the case of this tool, adding a failing test case looks trivial if you've got the URL of a page it fails on.
Provided the maintainer is willing to provide some minimal guidance to issue reporters who lack the necessary know-how, it even seems like a clever back door way of helping people learn to contribute to open source.
If this results in the project being easier to maintain and being maintained longer, then I’m fine with this.