AssetReference variable dropdown is not aligned with other variable type dropdowns in UI Builder

Steps to reproduce:

1. Create a new 3D URP project
2. Create a new UI Document (Assets > Create > UI Toolkit > UI Document)
3. Open the .uxml file in UI Builder
4. Create a new USS file with a new selector (e.g. "test")
5. Select the newly created selector
6. In the Inspector, expand the "Variables" foldout
7. Click the "+" icon and add "AssetReference" variable
8. (Optional) Add a few other variables to better observe their expected layout
9. Observe the "AssetReference" dropdown position

Actual results: The "AssetReference" dropdown appears in the middle/value section of the variable row instead of on the far right, causing the row layout to be inconsistent with the other variable entries

Expected results: The "AssetReference" dropdown appears on the very right of the row, aligned with other variable types dropdowns

Reproducible with versions: 6000.6.0a2, 6000.6.0a3

Not reproducible with versions: 6000.5.0b4, 6000.6.0a1

Tested on (OS): macOS 26.4, Ubuntu 24.04

Notes:

• This creates confusing UX due to the expected dropdown being in the wrong place