Support muxed connection in DisabledElector
GitLab's tests use Praefect with the DisabledElector. Recently an MR was merged to default enable all Gitaly and Praefect feature flags when the tests are being run. The pipeline was failign as the DisabledElector did not support the connection multiplexing and the feature flags were enabled. Fix this by passing the multiplexed connections in to the DisabledElector as well.