chore(server): Move cache miss log statement to debug level

This is very annoying otherwise.

tools/nixery/server/builder/cache.go

@@ -185,7 +185,7 @@ func layerFromCache(ctx context.Context, s *State, key string) (*manifest.Entry,
 		log.WithError(err).WithFields(log.Fields{
 			"layer":   key,
 			"backend": s.Storage.Name(),
-		}).Warn("failed to retrieve cached layer from storage backend")
+		}).Debug("failed to retrieve cached layer from storage backend")
 
 		return nil, false
 	}

tools/nixery/server/storage/filesystem.go

@@ -73,7 +73,7 @@ func (b *FSBackend) ServeLayer(digest string, r *http.Request, w http.ResponseWr
 
 	log.WithFields(log.Fields{
 		"layer": digest,
-		"path": p,
+		"path":  p,
 	}).Info("serving layer from filesystem")
 
 	http.ServeFile(w, r, p)