Make some fixes to logging in PVF subsystem (#6180)

* Log exit status code for workers

* Make log for execute job conclusion match prepare job conclusion

Trace log for conclusion of prepare job:

```rs
gum::debug!(
	target: LOG_TARGET,
	validation_code_hash = ?artifact_id.code_hash,
	?worker,
	?rip,
	"prepare worker concluded",
);
```

Co-authored-by: parity-processbot <>

polkadot/node/core/pvf/src/execute/queue.rs

@@ -247,9 +247,9 @@ fn handle_job_finish(
 	gum::debug!(
 		target: LOG_TARGET,
 		validation_code_hash = ?artifact_id.code_hash,
+		?worker,
 		worker_rip = idle_worker.is_none(),
-		?result,
-		"job finished.",
+		"execute worker concluded",
 	);
 
 	// First we send the result. It may fail due the other end of the channel being dropped, that's