WIP: fixup podvm_mkosi: try tar the qcow2

.github/workflows/podvm_mkosi.yaml

@@ -320,13 +320,14 @@ jobs:
           mkdir oras
           cd oras
           cp ../build/podvm-*.qcow2 .
+          tar cJf podvm.tar.xz podvm-*.qcow2
           image=${{ inputs.registry }}/podvm-generic-fedora
           if [ "${{inputs.debug}}" = "true" ]; then
             image=${image}-debug
           fi
           tag=${{ steps.image_tag.outputs.image_tag }}
           arch_tag=${tag}_${{ inputs.arch }}
-          oras push "${image}:${arch_tag}" podvm-*.qcow2
+          oras push "${image}:${arch_tag}" podvm.tar.xz
           # We need to create the platform annotations with docker, since oras 1.2 doesn't support
           # pushing with platform yet.
           docker manifest create "${image}:${tag}" --amend "${image}:${arch_tag}"