RunSubgraph Subgraph Variable don't pass assigned BehaviorGraph from the node

Steps to reproduce:

1. Install `com.unity.behavior` 1.0.6 or above
2. Create a three Behavior graphs (Nested Subgraph, Subgraph and Parent Graph)
3. Open Nested Subgraph: Add and Connect a Log Message node ("Hello World") to the On Start node.
4. Open Subgraph:
   1. Add and connect a sequence of Log Variable and Run Subgraph node to On Start.
   2. Add a blackboard variable of type `Subgraph` named "Nested Subgraph"
   3. Assign the subgraph variable to both the Log Variable} and {{Run Subgraph nodes
5. Open Graph:
   1. Add and connect Run Subgraph to On Start
   2. Assign the Subgraph graph asset to the Run Subgraph Node
   3. Inspect the Run Subgraph node and set the "Nested Subgraph" field with Nested Subgraph graph asset
6. Add the Parent Graph to a gameObject named "Agent" in the scene
7. Enter playmode

Expected Result
Console log contains:

1. `[Agent] Nested Subgraph = "Nested Subgraph"`
2. `Hello World`

Actual Result
Console log contains: `[Agent] Nested Subgraph = null`

Workaround
Always linked a blackboard variable instead of assigning subgraph directly on the Run Subgraph node inspector. (See https://discussions.unity.com/t/nested-dynamic-behavior-subgraphs/1699129/5).