Verified motion vector "decoding" against the auto-generated camera MVs based on the clip-space delta matrix, and made a small fix

Packages/com.unity.postprocessing@3.2.2/PostProcessing/Runtime/Effects/Upscaling/SGSR2/Shaders/sgsr2_birp.hlsl

@@ -21,6 +21,6 @@ SamplerState s_LinearClamp  : register(s1);
 
 inline float2 decodeVelocityFromTexture(float2 ev)
 {
-    // Nothing to do, motion vectors are not encoded
-    return ev;
+    // Nothing much to do, motion vectors are not encoded
+    return -ev;
 }