“Failed to load” window appears when a package’s docked window is opened and the package is uninstalled

Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Open the Timeline window (Window > Sequencing > Timeline)
3. Dock the Timeline window
4. Open the Package Manager (Window > Package Management > Package Manager)
5. Uninstall the Timeline package
6. Observe the Editor

Actual results: There is a “Failed to load” docked window

Expected results: The Timeline window is closed

Reproducible with versions: 2022.3.67f1, 6000.0.58f1, 6000.2.6f1, 6000.3.0b3, 6000.4.0a1

Tested on (OS): Ubuntu 24.04, macOS Silicon Sequoia 15.6.1

Notes:

• The "Failed to load" window can not be moved but can be closed