feat: don't crash when failing to create trigger message — radicle-ci-broker

Signed-off-by: Lars Wirzenius liw@liw.fi

 then stderr is exactly ""
 ~~~
 ## Fails run if building trigger fails, but does not crash
 _Want:_ The CI broker fails a CI run if it can't create a trigger
 message from a CI event, but it continues running and processing other
 events.
 _Why:_ If it's not possible to create a trigger message, the CI run
 can't succeed, unless the failure is temporary. However, we have no
 way of knowing if the failure is temporary, so the safe thing is to
 mark the CI run as having failed and removing the CI event from the
 queue. Further, the CI broker should not crash and should process
 other events.
 _Who:_ `cib-dev`
 A failure to create a trigger message happens if the CI event refers
 to a repository, commit, or Git ref that doesn't exist in the
 repository on the local node. This should not ever happen, as the CI
 event is only emitted by the node after the changes are on the node.
 However, it has happened due to a programming error in the CI broker.
 By handling the error and removing the event, the CI broker is a
 little bit more robust.
 We verify this by inserting two events into the queue and then running
 `cib queued` to process them. We arrange things so that the first
 event fails, but the second one succeeds.
 ~~~scenario
 given a Radicle node, with CI configured with broker.yaml and adapter dummy.sh
 given a Git repository xyzzy in the Radicle node
 given a directory reports
 when I run ./env.sh cibtool --db ci-broker.db event add --repo xyzzy --ref main --commit f42ea5cb9ce2dc7a9b87834ccee5b9bb3867db90 --kind branch-updated --base main
 when I run ./env.sh cibtool --db ci-broker.db event add --repo xyzzy --ref main --commit HEAD --kind branch-updated --base main
 when I run ./env.sh cib --config broker.yaml queued
 then stderr contains "f42ea5cb9ce2dc7a9b87834ccee5b9bb3867db90"
 when I run cibtool --db ci-broker.db run list
 then stdout has one line
 ~~~
 # Acceptance criteria for test tooling
 The event synthesizer is a helper to feed the CI broker node events in

     db::{QueueId, QueuedCiEvent},
     msg::Request,
     node_event_source::NodeEventSource,
     queueproc::QueueError,
     run::Run,
 };

     info!(kind = %Kind::GotEvent, ?id, ?event, "picked event from queue");
 }
 pub fn queueproc_processed_event(result: &Result<bool, QueueError>) {
     info!(kind = %Kind::GotEvent, ?result, "result of processing event");
 }
 pub fn queueproc_remove_event(id: &QueueId) {
     info!(kind = %Kind::Debug, ?id, "remove event from queue");
 }

             while let Some(qe) = self.pick_event()? {
                 self.run_tx.notify()?;
                 logger::queueproc_picked_event(qe.id(), &qe);
                 done = self.process_event(qe.event())?;
                 let res = self.process_event(qe.event());
                 logger::queueproc_processed_event(&res);
                 match res {
                     Ok(shut_down) => done = shut_down,
                     Err(QueueError::BuildTrigger(_, _)) => done = false,
                     Err(err) => Err(err)?,
                 }
                 self.drop_event(qe.id())?;
                 self.run_tx.notify()?;
             }