When changing a property in a custom pass prefab instance, the blue line that indicates a property override isn't displayed in HDRP, as well as the Apply / Revert options in the context menu.

Repro steps:
- Open a project with HDRP installed
- Create a custom pass with the menu Assets/Create/Volume/Custom Pass
- Add a 'FullScreen' custom pass to the custom pass list
- Make the custom pass object a prefab
- In the prefab instance (in the scene) change a property of the fullscreen custom pass (target camera buffer for example)
- Observe that the blue prefab override line doesn't show

Repro with Unity 2021.2.0b3 and HDRP 12.0
Doesn't repro with Unity 2020.3.8f1 and HDRP 10.5, Unity 2021.1.12f1