Steps to repro:
1. Create new project;
2. Open "SampleScene" scene;
3. Select File>New Scene;
4. In the appeared window select "Basic (Built-In)" and click "Create" button;
6. In the newly creted scene press "Generate Lighting" in Ligthing window;
7. Wait until lighting bakes.

Expected result:
After baking "Force stop" and "Cancel" buttons disappear and only "Generate Lighting" button is shown.
OR
"Generate Lighting" button should be grayed out until the user has either dirtied the scene or created the lighting settings asset manually and saved the scene.

Actual result:
"Force stop" and "Cancel" buttons don't disappear after finishing GI bake. See attached video.

Workaround is to either save the newly created scene, add any gameobject and rebake the GI (with saving the scene) or create the new Lighting Settings Asset file, save the scene and rebake.

Notes:
- Reproducible in Versions 2021.1.0a7, 2020.2.0b13, 2020.1.17f1, 2019.4.16f1;
- Not reproducible in Version 2018.4.30f1, because in that Version auto-baking mode was always on; Also in that version the popup window for saving the scene appears after disabling auto and manually rebaking, making the baking to finish properly.
- The issue got introduced with disabling the auto-baking mode for the new scene;
- Although the issue has a little impact on users, as it only happens when baking the empty scene, this might confuse some of the users makign them wondering why the baking didn't properly finish.