[2D][URP] Sprite Light 2D visuals don't update when Sprite texture is modified in transparent areas.

Repro steps:
- Open the PNG files for either of the sprites that are referenced by the 2 sprite lights in the scene.
- Edit them in an image-editing tool (Photoshop) by adding new pixels in transparent areas outside the white triangle.
- Save and return to Unity.
- Observe that the light visuals have not changed.
Note:
- Removing and re-adding the sprite references works as expected.
- Modifying pixels that are already visible (inside the white triangle) works as expected.

Expected result: Sprite light updates its texture when its referenced sprite is edited
Actual result: Sprite light does not update its texture when its referenced sprite is edited until it is re-added