fix: handle invalid json in node events — radicle-ci-broker

Previously, radicle-ci-broker crashed whenever it received an event from radicle-node which it could not parse, for example because a new event type has been added to radicle-node, but the radicle crate radicle-ci-broker depended on didn’t contain this new variant yet.

             }
             Err(err) => {
                 logger::error("error reading event from node", &err);
                 Err(CiEventSourceError::NodeEventError(err))
                 if let NodeEventError::Node(radicle::node::Error::InvalidJson { .. }) = err {
                     Ok(Some(Vec::new()))
                 } else {
                     Err(CiEventSourceError::NodeEventError(err))
                 }
             }
             Ok(None) => {
                 logger::ci_event_source_end();