Subgraph Operators cannot be dragged and dropped to Subgraph blocks from Project window

How to reproduce:

1. Import the attached package
2. Open Subgraph Block.vfx
3. Drag and drop Oprator.vfx to Block.vfx

Actual result: Operator.vfx is not dropped to the graph view once RMB is released

Expected result: Operator.vfx is dropped to the graph view once RMB is released

Reproduced with: 2023.1.0a12

Notes: 

• Works fine when drag & dropping operator to anotehr operator's graph view
• Operator can be added to the Block's graphview through the node search