Run the tests from matrix-sdk-ffi inside the CI

As a follow-up from https://github.com/matrix-org/matrix-rust-sdk/pull/3814

> Tests from `matrix-sdk-ffi` aren't run in the CI as far as I remember. Is it possible to move some of this logic inside `matrix-sdk` maybe? I understand though that the code you're testing are specific to Element, and should not leave in `matrix-sdk` itself 🤔.
>
> We may want to run the tests from `matrix-sdk-ffi` inside the CI then.
>
> Can you open an issue, or better, a pull request, to not forget about that please?

Start by reviewing the CI configuration and the matrix-sdk-ffi crate, using pull request 3814 for context on the requested follow-up. Determine how the existing CI invokes matrix-sdk tests, then ensure the matrix-sdk-ffi tests run there and verify the CI job passes.

Written by the indexing model from the issue text.