remove unneeded slice

Signed-off-by: Meredith Lancaster <malancas@github.com>

pkg/cmd/attestation/artifact/digest/digest.go

@@ -49,5 +49,5 @@ func CalculateDigestWithAlgorithm(r io.Reader, alg string) (string, error) {
 		return "", fmt.Errorf("failed to calculate digest: %w", err)
 	}
 	digest := h.Sum(nil)
-	return hex.EncodeToString(digest[:]), nil
+	return hex.EncodeToString(digest), nil
 }