Animation window scrollbar keeps resetting when the scrollbar width is changed after adding an event

Steps to reproduce:

1. Create a new project using the Universal 3D template
2. Create a new Cube GameObject (GameObject > 3D Object > Cube)
3. Select the newly created Cube GameObject in the Hierarchy window
4. Open the Animation window (Window > Animation > Animation)
5. Dock the Animation window
6. Create a new Animation
7. Add event anywhere in the Animation
8. Resize the bottom scrollbar to be as small as possible
9. Drag the scrollbar to the left
10. Observe the Animation window

Actual results: The scrollbar is jittery, resizes on its own or gets reset

Expected results: The scrollbar is dragged to the left and nothing else happens

Reproducible with versions: 6000.0.68f1, 6000.3.10f1, 6000.4.0b9, 6000.5.0a7

Tested on (OS): MacOS Silicon Tahoe 26.2, Ubuntu 24.04