Adapt to changes in libyang-cpp (instance-identifier)

Change-Id: I78ed24521305d50154fa32e3e14a1ee7fbc3c599
Depends-on: https://gerrit.cesnet.cz/c/CzechLight/dependencies/+/6439
Depends-on: https://gerrit.cesnet.cz/c/CzechLight/cla-sysrepo/+/6440
diff --git a/src/libyang_utils.cpp b/src/libyang_utils.cpp
index b09454e..09676d6 100644
--- a/src/libyang_utils.cpp
+++ b/src/libyang_utils.cpp
@@ -40,7 +40,7 @@
         return dec.number * std::pow(10, -dec.digits);
     }
 
-    leaf_data_ operator()(const std::optional<libyang::DataNode>&) const
+    leaf_data_ operator()(const libyang::InstanceIdentifier&) const
     {
         throw std::runtime_error("instance-identifier is not supported");
     }