* fetch RiseupVPN CA cert with MultiGetter. It allows us to write better tests and ensures this test step is added in the logs
* Implement TransportStatus for RiseupVPN tests. It indicates if a whole transport is blocked, which is considered as a test anomaly
* Redesign unit tests for RiseupVPN. Instead of a real backend, mocked server responses are used. Tests for invalid CA certs and for TransportStatus are added.
* Update internal/engine/experiment/riseupvpn/riseupvpn.go
Co-authored-by: Simone Basso <bassosimone@gmail.com>