Fix Barracuda assembly reference. (#3993)

com.unity.ml-agents/Tests/Editor/PublicAPI/Unity.ML-Agents.Editor.Tests.PublicAPI.asmdef

     "references": [
         "Unity.ML-Agents.Editor",
         "Unity.ML-Agents",
-        "Barracuda",
+        "Unity.Barracuda",
         "Unity.ML-Agents.CommunicatorObjects"
     ],
     "optionalUnityReferences": [