Do not allow version with digest

Signed-off-by: Terry Howe <terrylhowe@gmail.com>

pkg/registry/util.go

@@ -31,6 +31,7 @@ import (
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
+	errdef "oras.land/oras-go/pkg/content"
 	orascontext "oras.land/oras-go/pkg/context"
 	"oras.land/oras-go/pkg/registry"
 
@@ -135,6 +136,9 @@ func parseReference(raw string) (registry.Reference, error) {
 	}
 	parts := strings.Split(raw, ":")
 	if len(parts) > 1 && !strings.Contains(parts[len(parts)-1], "/") {
+		if len(digest) > 0 {
+			return registry.Reference{}, fmt.Errorf("%w: specify digest or version", errdef.ErrInvalidReference)
+		}
 		tag := parts[len(parts)-1]
 
 		if tag != "" {