Add Missing Fallback Setting for FSR EASU Shader

This change updates the FSR EASU shader to declare that no fallback shader is provided. The C# code explicitly handles this situation already and will never draw anything with the shader when it's unsupported.

Author: gmitrano-unity

Packages/com.unity.render-pipelines.universal/Shaders/PostProcessing/EdgeAdaptiveSpatialUpsampling.shader

@@ -62,4 +62,6 @@ Shader "Hidden/Universal Render Pipeline/Edge Adaptive Spatial Upsampling"
             ENDHLSL
         }
     }
+
+    Fallback Off
 }