Multiple "Add a graph node" windows can be opened in Graph Toolkit when the graph is freshly imported

Steps to reproduce:

1. Create a new project using Universal 3D template
2. Import the attached "MySimpleGraph.cs" into the Project
3. Go to Assets > Create > Graph Toolkit Samples > Simple Graph
4. Open the created graph
5. Right-click on empty space and select "Add Node"
6. Repeat 5th step
7. Observe additional "Add a graph node" window opens
8. Press "Space" on the keyboard
9. Observe another additional  "Add a graph node" window opens

Actual results: There is an unlimited amount of "Add a graph node" windows that can be opened

Expected results: Only one "Add a graph node" window should be open at a time

Reproducible with versions: 6000.4.1f1, 6000.5.0b1, 6000.6.0a1

Can’t test with versions: 6000.3.12f1 (Graph Toolkit errors)

Tested on (OS): Ubuntu 24.04 (reproducible), macOS 26.3 (not reproducible)

Notes:

• After some time in the Editor, the issue may stop reproducing
• For best reproduction results, import the graph script and create the graph asset fresh in a new project/session