Remove let _ = (#5436)

## Motivation

Missed a `let _ = ` on
#5431

## Proposal

Remove it

## Test Plan

CI

Author: ndr-ds

linera-service/src/task_processor.rs

@@ -270,7 +270,12 @@ impl<Env: linera_core::Environment> TaskProcessor<Env> {
                     }
                     // Signal that this batch is done so the main loop can process
                     // the next batch for this application.
-                    let _ = sender.send(TaskMessage::BatchComplete { application_id });
+                    if sender
+                        .send(TaskMessage::BatchComplete { application_id })
+                        .is_err()
+                    {
+                        error!("Outcome receiver dropped for {application_id}");
+                    }
                 });
             }
         }