testing/topgrade: move to new project and upgrade to 10.2.4

The author of the original archived the repo (https://github.com/r-darwish/topgrade) and linked to this new one (https://github.com/topgrade-rs/topgrade).

In the readme they stated:

This repository is no longer maintained. An effort was made by the community to keep maintaining the project at https://github.com/topgrade-rs/topgrade. I am not involved in this effort nor do I know the people behind it, so I encourage you to inspect their work before using the fork.

But it seems to be fine, the original author even committed to the new project: https://github.com/topgrade-rs/topgrade/commit/cba9dc1c2ce8b37e0dca5e3288f753b1fb6483e4