Fix: Use after free in geometry node group logger

The name of the node group in the geometry nodes logger is created
in `GeoModifierLog::get_local_tree_logger`, where it references the
compute context. However, the compute context is a local variable
that doesn't live as long as the log. Therefore the log needs to own
the node group name.

Removing the ownership from `NodeGroupComputeContext` may be
possible as well, but seems less obviously correct. This can be a
temporary solution until we can completely avoid storing strings
in the logger (see D15775).

Fixes T101599

source/blender/nodes/NOD_geometry_nodes_log.hh

@@ -169,7 +169,7 @@ using TimePoint = Clock::time_point;
 class GeoTreeLogger {
  public:
   std::optional<ComputeContextHash> parent_hash;
-  std::optional<StringRefNull> group_node_name;
+  std::optional<std::string> group_node_name;
   Vector<ComputeContextHash> children_hashes;
 
   LinearAllocator<> *allocator = nullptr;