Update config.json

tests/validation/config.json

@@ -633,7 +633,7 @@
         },
         {
             "title": "GLTF Alpha Blend",
-            "playgroundId": "#SYQW69#578",
+            "playgroundId": "#SYQW69#579",
             "referenceImage": "glTFAlphaBlend.png",
             "renderCount": 1
         },
@@ -1019,4 +1019,4 @@
             "referenceImage": "shadowsinstancesright.png"
         }
     ]
-}
+}