Update barracuda to 2.0.0-pre.3, update ml-agents to pre.3.

DevProject/Packages/packages-lock.json

 {
   "dependencies": {
     "com.unity.barracuda": {
-      "version": "2.0.0-pre.2",
+      "version": "2.0.0-pre.3",
       "depth": 1,
       "source": "registry",
       "dependencies": {
       "depth": 0,
       "source": "local",
       "dependencies": {
-        "com.unity.barracuda": "2.0.0-pre.2",
+        "com.unity.barracuda": "2.0.0-pre.3",
         "com.unity.modules.imageconversion": "1.0.0",
         "com.unity.modules.jsonserialize": "1.0.0"
       }
       "depth": 0,
       "source": "local",
       "dependencies": {
-        "com.unity.ml-agents": "2.0.0-pre.2",
+        "com.unity.ml-agents": "2.0.0-pre.3",
         "com.unity.modules.physics": "1.0.0"
       }
     },

Project/Packages/packages-lock.json

       "depth": 0,
       "source": "local",
       "dependencies": {
-        "com.unity.ml-agents": "2.0.0-pre.2",
+        "com.unity.ml-agents": "2.0.0-pre.3",
         "com.unity.modules.physics": "1.0.0"
       }
     },

com.unity.ml-agents.extensions/package.json

   "unity": "2019.4",
   "description": "A source-only package for new features based on ML-Agents",
   "dependencies": {
-    "com.unity.ml-agents": "2.0.0-pre.2",
+    "com.unity.ml-agents": "2.0.0-pre.3",
     "com.unity.modules.physics": "1.0.0"
   }
 }

com.unity.ml-agents/CHANGELOG.md

 and this project adheres to
 [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
-## [2.0.0-pre.2] - 2021-04-22
+## [2.0.0-pre.3] - 2021-04-22
+- update Barracuda to 2.0.0-pre.3.
 - The minimum supported Unity version was updated to 2019.4. (#5166)
 - Several breaking interface changes were made. See the
 [Migration Guide](https://github.com/Unity-Technologies/ml-agents/blob/release_17_docs/docs/Migrating.md) for more

com.unity.ml-agents/Runtime/Academy.cs

         /// Unity package version of com.unity.ml-agents.
         /// This must match the version string in package.json and is checked in a unit test.
         /// </summary>
-        internal const string k_PackageVersion = "2.0.0-pre.2";
+        internal const string k_PackageVersion = "2.0.0-pre.3";
 
         const int k_EditorTrainingPort = 5004;
 

com.unity.ml-agents/package.json

 {
   "name": "com.unity.ml-agents",
   "displayName": "ML Agents",
-  "version": "2.0.0-pre.2",
+  "version": "2.0.0-pre.3",
-    "com.unity.barracuda": "2.0.0-pre.2",
+    "com.unity.barracuda": "2.0.0-pre.3",
     "com.unity.modules.imageconversion": "1.0.0",
     "com.unity.modules.jsonserialize": "1.0.0"
   }

utils/validate_versions.py

             f.write(new_contents)
 
     if csharp_version is not None:
-        package_version = f"{csharp_version}-pre.2"
+        package_version = f"{csharp_version}-pre.3"
         if csharp_extensions_version is not None:
             # since this has never been promoted we need to keep
             # it in preview forever or CI will fail