This updates github.com/opencontainers/image-spec/schema subpackage from an obsolete
.../jsonschema/v5 to /v6 .
We use these dependencies only in tests, so it doesn't matter that much,
but removing references to years-old unmaintained versions makes it easier to check
/ remove other such cases.
(This is test-only, so the added files in vendor/ do not mean a larger binary
size; it's almost exactly unchanged.)
Signed-off-by: Miloslav Trmač <mitr@redhat.com>
