Save Scene pop up does not close after clicking on Don't Save button on Enabling Use incremental GC.
Save Scene pop up appears twice on clicking "Don't Save" button on enabling Use incremental GC.

Steps to repro:
1. Create a new project.
2. GameObject > 3D > Cube.
3. File > Build Settings > Player Settings > Other Settings.
4. Enable "Use incremental GC" > Apply > Don't Save > Click on Cancel.

There are two scenarios to repro this issue:
1. Click on Cancel button.
2. Click on Close button(X).

Actual Result:
Save Scene pop up does not close after clicking on Don't Save button.

Expected Result:
Save Scene pop up should be closed.

Reproducible with:
2020.1.0a15, 2020.1.0a4, 2019.3.0f1, 2019.3.0b4.

NOTE: Save pop up is introduced:
- in 2020.1 from 2020.1.0a4.
- in 2019.3 from 2019.3.0b4.

Environment:
Windows 10 & Mac 10.14.