Required icons in the Icon Browser has a “Delete” option in the context menu when these icons cannot be deleted and nothing happens when clicked

Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Install the App UI package (com.unity.dt.app-ui)
3. Open the Icon Browser window (Window > App UI > Icon Browser)
4. Create a new App UI Icons style sheet
5. Enable the "Show required icons" by ticking the checkbox
6. Right-click any of the icons
7. Click the "Delete selected icons" option
8. Observe the Icon Browser window

Actual results: Required icons cannot be deleted and nothing happens when clicking the delete button

Expected results: There is no delete button for the required icons

Reproducible with versions: 2.1.10 (6000.0.76f1, 6000.3.17f1, 6000.4.10f1, 6000.5.0b11, 6000.6.0a6)

Tested on (OS): MacOS Silicon Tahoe 26.3