UI Toolkit UI Documents are not unloaded correctly when switching Scenes

Reproduction steps:
1. Open the user’s attached project
2. Enter Play Mode
3. Press the “space” button to enter the next Scene (notice it has UI elements)
4. Press the “space” button to change the Scene again
5. Open Window > Analysis > Memory Profiler
6. Capture New Snapshot
7. Go to Memory breakdown and notice that “halftone” and “noisebox” are still using memory

Expected result: Unused objects are cleaned from memory after changing Scenes
Actual result: Objects used in the earlier Scene are not cleaned from memory

Reproducible with: 2020.3.40f1, 2021.3.11f1, 2022.1.20f1, 2022.2.0b10, 2023.1.0a14

Reproducible on: Windows 10