Steps to reproduce:
1. Create a new HDRP project
2. Navigate to Assets/Scenes and open "samplescene.unity" in any text editor
3. Hit Ctrl + F and search for "m_SkySettings"
4. Take note of the FileID value
5. In Unity, enter and exit Play Mode
6. Dirty the scene by disabling and then reenabling any GameObject
7. Save the Scene
8. Repeat steps 2 to 4

Expected result: m_SkySettings FileID value remains the same
Actual result: m_SkySettings field is serialized, therefore its value is changed every time a scene is dirtied

Reproduced in: HDRP 7.0.1 (2019.3.0a12), HDRP 7.3.1 (2020.3.7f1), HDRP 8.0.1 (2020.2.0a4)
Not reproducible in: HDRP 7.0.0 (2019.3.0a11)
Could not test with: HDRP preview - 6.9.2 and older (m_SkySettings field unavailable)