node: Add session token's key decoding error details

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

pkg/services/container/morph/executor.go

@@ -361,7 +361,7 @@ func (s *morphExecutor) validateToken(t *sessionV2.Token, cIDV2 *refs.ContainerI
 
 	err = keyFromToken.Decode(t.GetSignature().GetKey())
 	if err != nil {
-		return errors.New("error while decoding public key from the token's signer")
+		return fmt.Errorf("error while decoding public key from the token's signer: %w", err)
 	}
 
 	userFromToken := user.ResolveFromECDSAPublicKey(ecdsa.PublicKey(keyFromToken))