Don't determine default tag if bundles is referenced using digest

If a bundle is referenced explicitly using a tag or a digest, we should
not try to use the default tag

Signed-off-by: Kim Christensen <kimworking@gmail.com>

pkg/cnab/extended_bundle.go

@@ -376,8 +376,8 @@ func (b *ExtendedBundle) ResolveVersionv2(name string, dep v2.Dependency) (OCIRe
 	}
 
 	if dep.Version == "" {
-		// Check if they specified an explicit tag in referenced bundle already
-		if ref.HasTag() {
+		// Check if they specified an explicit tag or digest in referenced bundle already
+		if ref.HasTag() || ref.HasDigest() {
 			return ref, nil
 		}