[unity] Fixed URP 2D Sprite shader not respecting straight alpha blend modes. Closes #1755.

spine-unity/Modules/com.esotericsoftware.spine.urp-shaders/Shaders/2D/Include/Spine-Sprite-StandardPass-URP-2D.hlsl

@@ -104,7 +104,7 @@ half4 CombinedShapeLightFragment(VertexOutputSpriteURP2D input) : SV_Target
 #endif
 
 	APPLY_EMISSION(pixel.rgb, input.texcoord)
-
+	pixel = prepareLitPixelForOutput(pixel, input.vertexColor);
 	COLORISE(pixel)
 	return pixel;
 }