chore: use Labgrid tarball from fork

We need to use our fork until the upstream PR[1] is merged. As a
side-effect, we're upgrading from 24.0a1 to the latest upstream `master`.

This will break some of our [unused] code which depends on crossbar,
given the latest Labgrid uses gRPC. We can fix that later.

[1]: https://github.com/labgrid-project/labgrid/pull/1558