32be2d9067
To test current buildx we need a later skopeo that understands the OCI manifest formats. c.f. the zuul-executor image updates with Iab667a92a5b6e6f8591db2aa435a782913d9d34f. A recent enough version (1.9) isn't packaged for any LTS distros. So add an upstream option, but it's only implemented (for now) on Jammy, where we will test with it. Change-Id: I206a3cbfb16575f409771d96c2b7e49929e61a49