1. What happened
[2D][Polygon Collider 2D] Sprite could not be dragged onto a Polygon Collider component anymore

2. How we can reproduce it using the example you attached

Repro Steps
1. Open Attached Project.
2. Click on the Sprite in Assets folder and drag it into Polygon Collider component in Inspector
3. Note that Sprite could not be dragged onto a Polygon Collider component anymore

Expected Behaviour: User was able to drag a sprite into a polygon collider 2D and the Collider would change into the Sprite's Shape