Fix: memory leak after type conversion in geometry nodes group

The leak happened when two things were true:
* Inside of a node group a socket is linked to a Group Input that has
  a different type.
* The corresponding input on the parent Group node is not linked.

The conversion happened correctly, but the original value wasn't
destructed.

source/blender/modifiers/intern/MOD_nodes_evaluator.cc

@@ -1455,6 +1455,7 @@ class GeometryNodesEvaluator {
     }
     void *converted_buffer = allocator.allocate(required_type.size(), required_type.alignment());
     this->convert_value(type, required_type, buffer, converted_buffer);
+    type.destruct(buffer);
     return {required_type, converted_buffer};
   }