csharp: Do not use the System Bus for testing.

Summary: To allow the C# bindings running on the CI

Reviewers: zmike, brunobelo, felipealmeida, segfaultxavi, stefan_schmidt

Reviewed By: stefan_schmidt

Subscribers: cedric, reviewers, committers

Tags: efl

Maniphest Tasks: T8313

Differential Revision: https://phab.enlightenment.org/D10283