Steps to reproduce:
1. Open or create a project
2. Go to "Window" ->"Package Manager"
3. Go to the "My Assets" section
4. If you don't have any assets please download them (for example "Realistic Tree 9 [Rainbow Tree]")
5. Click on a "+" on the import button

6. In the "Import Unity Package" window click "None"
7. Verify, that all items become unchecked but the "Import" button stays active.

Expected result: The import button is active, the user can click it, and if he clicks it nothing happens. Added screenshot in the "Attachments" section.
Actual result: If there are no items selected for the import "Import" button should be displayed as disabled. And when the user selects an item or a few of them, the button should become active.

Reproducible with: 2023.2.0a23, 2023.1.2f1, 2022.3.4f1, 2021.3.28f1.