Bug#993487: libguestfs-tools: virt-sparsify fails to pass necessary arguments to qemu-img

[Aleksey I. Zavilohin]

Confirm this problem with qemu 6.1

https://wiki.qemu.org/ChangeLog/6.1
Section: Incompatible changes

When creating an image with a backing file, or changing the backing file 
of an existing image, qemu-img requires now that the backing file format 
is specified as well.

with qemu 6.0 works fine

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Aleksey I. Zavilohin
+7-9028968180