Fix health check spamming the expiry index

das/local_file_storage_service.go

@@ -229,7 +229,14 @@ func (s *LocalFileStorageService) String() string {
 
 func (s *LocalFileStorageService) HealthCheck(ctx context.Context) error {
 	testData := []byte("Test-Data")
-	err := s.Put(ctx, testData, uint64(time.Now().Add(time.Minute).Unix()))
+	// Store some data with an expiry time at the start of the epoch.
+	// If expiry is disabled it will only create an index entry for the
+	// same timestamp each time the health check happens.
+	// If expiry is enabled, it will be cleaned up each time the pruning
+	// runs. There is a slight chance of a race between pruning and the
+	// Put and Get calls, but systems using the HealthCheck will just retry
+	// and succeed the next time.
+	err := s.Put(ctx, testData /* start of epoch */, 0)
 	if err != nil {
 		return err
 	}