Pass task name into item metrics, not task object

src/kernel.js

@@ -80,10 +80,10 @@ module.exports = async function createKernel(_configuration) {
 					simpleSink(({ status }) => {
 						if (status === "completed") {
 							metrics.successfulItems.inc(1);
-							metrics.successfulItems.labels({ task: task }).inc(1);
+							metrics.successfulItems.labels({ task: task.name }).inc(1);
 						} else if (status === "failed") {
 							metrics.failedItems.inc(1);
-							metrics.failedItems.labels({ task: task }).inc(1);
+							metrics.failedItems.labels({ task: task.name }).inc(1);
 						} else {
 							unreachable(`Unrecognized status '${status}'`);
 						}