Fix the cubemap GGX convolution

Assets/ScriptableRenderLoop/HDRenderLoop/Sky/Resources/GGXConvolve.shader

 
             half4 Frag(Varyings input) : SV_Target
             {
-                float3 N = input.eyeVector;
+                // Vector interpolation is not magnitude-preserving.
+                float3 N = normalize(input.eyeVector);
                 float3 V = N;
 
                 float perceptualRoughness = mipmapLevelToPerceptualRoughness(_Level);