“+” button remains active in the "Active Targets" section when no additional items are available for selection

Steps to reproduce:

1. Create a new Unity project
2. Open the "Create new Shader Graph Asset" window (Project window > right click > Create > Shader Graph > From Template...)
3. Select any template and click the "Create" button
4. Select a newly created shader graph item in the "Project" window
5. In the shader graph window, find "Graph Inspector"
6. Find the "Active Targets" section in the "Graph Inspector" section
7. Click "+" and select "Custom Render Texture"
8. Click "+" and select "Built-In"
9. Click "+" one more time and observe the result

Actual results: The “+” button is displayed as active and clickable even when there are no additional items available to select

Expected results: The “+” button is disabled when no additional items are available for selection, preventing further interaction

Reproducible with versions: 6000.3.10f1, 6000.4.0b10, 6000.5.0a7

Tested on (OS):  macOS - Tahoe 26.2