When storeLayer.Parent returns the parent layer, it needs to use the same logic as Get where it wraps in a describablyStoreLayer if the layer is describable. Otherwise, on Windows, this can result in pushing the foreign layers, which is not supposed to be allowed.
This fixes https://github.com/docker/docker/issues/30080.
Signed-off-by: Stefan J. Wernli <swernli@microsoft.com>