fix: handle invalid json in node events

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.

src/ci_event_source.rs

@@ -30,7 +30,11 @@ impl CiEventSource {
             }
             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();