registry: only update status on status update

Prior to this commit, we'd send updates to both the labels and the
cloud-provider whenever an update to the status of a build would be
sent.

This would cause a bug in which once a build reached the post-processing
state, and its cloud-provider was set, the status could not be updated
anymore, as the cloud-provider would be set and further updates are
rejected by the platform.

To avoid this problem, we only transmit the status when doing a status
update, and no other fields along with it.

internal/registry/types.bucket.go

@@ -156,10 +156,10 @@ func (b *Bucket) UpdateBuildStatus(ctx context.Context, name string, status mode
 	_, err = b.client.UpdateBuild(ctx,
 		buildToUpdate.ID,
 		buildToUpdate.RunUUID,
-		buildToUpdate.CloudProvider,
 		"",
 		"",
-		buildToUpdate.Labels,
+		"",
+		nil,
 		status,
 		nil,
 	)