CI: change hierarchy of bucket image
CI: change hierarchy of bucket image

Now we have a folder for x86_64 and one for aarch64.

Signed-off-by: Diana Popa <4240422768c1b315e51818a074064501037757cd@amazon.com>

firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker