gc: fix test cases since umoci GC is more strict

umoci GC enforces a valid index.json and current tests were a little
lax.

pkg/storage/storage.go

@@ -15,9 +15,9 @@ import (
 	"github.com/anuvu/zot/errors"
 	zlog "github.com/anuvu/zot/pkg/log"
 	guuid "github.com/gofrs/uuid"
+	"github.com/openSUSE/umoci"
 	godigest "github.com/opencontainers/go-digest"
 	ispec "github.com/opencontainers/image-spec/specs-go/v1"
-	"github.com/openSUSE/umoci"
 	"github.com/rs/zerolog"
 )
 
@@ -335,6 +335,11 @@ func (is *ImageStore) PutImageManifest(repo string, reference string, mediaType
 		return "", errors.ErrBadManifest
 	}
 
+	if m.SchemaVersion != 2 {
+		is.log.Error().Int("SchemaVersion", m.SchemaVersion).Msg("invalid manifest")
+		return "", errors.ErrBadManifest
+	}
+
 	for _, l := range m.Layers {
 		digest := l.Digest
 		blobPath := is.BlobPath(repo, digest)