Fixed a regression in the transparent SSR color pyramid usage. (#6001)

* Fixed a regression in the transparent SSR color pyramid usage.

* Update CHANGELOG.md

Co-authored-by: sebastienlagarde <sebastien@unity3d.com>

Author: anisunity

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/HDRenderPipeline.LightLoop.cs

@@ -1123,7 +1123,9 @@ TextureHandle RenderSSR(RenderGraph renderGraph,
                     BuildCoarseStencilAndResolveIfNeeded(renderGraph, hdCamera, resolveOnly: true, ref prepassOutput);
                 }
 
-                RTHandle colorPyramidRT = transparent ? hdCamera.GetCurrentFrameRT((int)HDCameraFrameHistoryType.ColorBufferMipChain) : hdCamera.GetPreviousFrameRT((int)HDCameraFrameHistoryType.ColorBufferMipChain);
+                // The first color pyramid of the frame is generated after the SSR transparent, so we have no choice but to use the previous
+                // frame color pyramid (that includes transparents from the previous frame).
+                RTHandle colorPyramidRT = hdCamera.GetPreviousFrameRT((int)HDCameraFrameHistoryType.ColorBufferMipChain);
                 if (colorPyramidRT == null)
                     return renderGraph.defaultResources.blackTextureXR;