Set "startAt" in skip case

Fix issue: #2416

The root cause is in skipped case, entrypoint do not write startedAt to Termination file.
That's means when reconcile of taskrun try to update startedAt, they found nothing, and the result is the startedAt will keep as the startedAt in pod.

pkg/entrypoint/entrypointer.go

@@ -82,15 +82,25 @@ type PostWriter interface {
 func (e Entrypointer) Go() error {
 	prod, _ := zap.NewProduction()
 	logger := prod.Sugar()
+
+	output := []v1alpha1.PipelineResourceResult{}
 	defer func() {
+		if wErr := termination.WriteMessage(e.TerminationPath, output); wErr != nil {
+			logger.Fatalf("Error while writing message: %s", wErr)
+		}
 		_ = logger.Sync()
 	}()
-	output := []v1alpha1.PipelineResourceResult{}
+
 	for _, f := range e.WaitFiles {
 		if err := e.Waiter.Wait(f, e.WaitFileContent); err != nil {
 			// An error happened while waiting, so we bail
 			// *but* we write postfile to make next steps bail too.
 			e.WritePostFile(e.PostFile, err)
+			output = append(output, v1alpha1.PipelineResourceResult{
+				Key:   "StartedAt",
+				Value: time.Now().Format(time.RFC3339),
+			})
+
 			return err
 		}
 	}
@@ -115,9 +125,7 @@ func (e Entrypointer) Go() error {
 			logger.Fatalf("Error while handling results: %s", err)
 		}
 	}
-	if wErr := termination.WriteMessage(e.TerminationPath, output); wErr != nil {
-		logger.Fatalf("Error while writing message: %s", wErr)
-	}
+
 	return err
 }