Background Image type in UI Builder falls back to "Texture" if no reference is set and the element is reselected

Steps to reproduce:

1. Create and open a new project
2. Create and open a new UI Document file in UI Builder
3. Create a VisualElement in UI Builder's Hierarchy
4. Select the VisualElement
5. Change the Background Image type to "Render Texture"
6. Deselect and select the VisualElement again
7. Observe the UI Builder's Inspector

Actual results: After step 4, the UXML is not made dirty, and after step 6, the Background Image type changes back to 'Texture'

Expected results: After step 4, the UXML is made dirty, and after step 6, the Background Image type stays on 'Render Texture'

Reproducible with versions: 2023.1.0a10, 6000.0.73f1, 6000.3.14f1, 6000.4.5f1, 6000.5.0b6, 6000.6.0a4

Tested on (OS): Windows 11 Pro, Ubuntu 24.04

Notes:

• Also reproducible with USS selectors