Steps to reproduce:
1. Open the “SerializedReference-multi-selection” project
2. Select one of two SerializedObject assets in the Assets folder and observe the Inspector window
3. Select both SerializedObject assets in the Assets folder and observe the Inspector window

Expected result: The foldout is the same as when selecting only one asset
Actual result: The arrows are always horizontal even if it's unfolded, and hovering with the mouse changes the arrow to a multiple-different checkbox

Reproducible with: 2021.3.22f1, 2022.2.13f1, 2023.1.0b10, 2023.2.0a8
Could not test with: 2020.3.46f1 (“The list of [SerializeReference] objects being deserialized is from a more recent version of Unity.” error is thrown)

Reproduced on: macOS Monterey 12.2 (Intel), Windows 11 (by user)