For importing Scaleway images, extension needs to be '.qcow2'
See: https://www.scaleway.com/en/docs/compute/instances/how-to/snapshot-import-export-feature/
> Make sure that the QCOW / QCOW2 image file you want to import,
> uses the file extension .qcow or .qcow2 to avoid issues while importing the image.
Signed-off-by: Mathieu Tortuyaux <mtortuyaux@microsoft.com>