"Assertion failed on expression" error is thrown when closing the Animator window with a deleted GameObject that had animations

Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Create a new Cube GameObject (GameObject > 3D Object > Cube)
3. Open the Animation window (Window > Animation > Animation)
4. Create a new Animation for the Cube GameObject
5. Open the Animator window (Window > Animation > Animator)
6. Delete the Cube GameObject from the Hierarchy window
7. Close the Animator window
8. Observe the Console window

Actual results: "Assertion failed on expression: '!dest.m_MultiFrameGUIState.m_Windows'" error is thrown

Expected results: No errors are thrown

Reproducible with versions: 6000.3.0a3, 6000.3.0a5

Not reproducible with versions: 6000.0.56f1, 6000.1.16f1, 6000.2.1f1, 6000.3.0a2

Tested on (OS): macOS Silicon Sequoia 15.6