Update TagLightingForSSS()

ScriptableRenderPipeline/Core/ShaderLibrary/CommonMaterial.hlsl

 // It can be accomplished by reading the stencil buffer.
 // A faster solution (which avoids an extra texture fetch) is to simply make sure that
 // all pixels which belong to an SSS material are not black (those that don't always are).
+// We choose the blue color channel since it's perceptually the least noticeable.
-    subsurfaceLighting.r = max(subsurfaceLighting.r, HALF_MIN);
+    subsurfaceLighting.b = max(subsurfaceLighting.b, HALF_MIN);
     return subsurfaceLighting;
 }
 
-    return subsurfaceLighting.r > 0;
+    return subsurfaceLighting.b > 0;
 }
 
 // MACRO from Legacy Untiy