Make sure the sky pass does not modify the alpha channel

Assets/ScriptableRenderLoop/HDRenderLoop/Sky/ProceduralSky/Resources/SkyProcedural.shader

         {
             ZWrite Off
             ZTest LEqual
-            Blend One OneMinusSrcAlpha
+            Blend One OneMinusSrcAlpha, Zero One
 
             HLSLPROGRAM
             #pragma target 5.0