[ty] Make a server snapshot less painful to update

[AlexWaygood]

Summary

Currently this snapshot feels like it causes quite a lot of development pain (at least for me), because I never think to run the ty_server tests if all I'm doing is adding a new diagnostic to the ty_python_semantic crate. So I always push my PR and only remember that there's this snapshot that also needs to be updated when CI starts failing on my PR.

This PR adds a new filter to the snapshot so that the snapshot no longer lists every rule that ty has, meaning that the snapshot no longer needs to be updated every time we add a new diagnostic to ty_python_semantic.

Test Plan

cargo test -p ty_server