[2D][Sprite] Upgrading project from 20.3 to 21.1 causes default sprite in scene to lose reference

Upgrading project from 20.3 to 21.1 causes default sprite in scene to lose reference due to change in asset guid

Repro steps:
1. In attached project, open SampleScene
2. Observe Square gameobject in scene lost its Sprite reference

Expected result: Default gameobjects in scene should keep their Sprite references when upgrading editor versions
Actual result: Default gameobjects in scene do not keep their Sprite references when upgrading editor versions