fix compile warnings for using obsolete enum (#4812)

com.unity.ml-agents/CHANGELOG.md

 
 ### Bug Fixes
 #### com.unity.ml-agents (C#)
+- Fix a compile warning about using an obsolete enum in `GrpcExtensions.cs`. (#4812)
 #### ml-agents / ml-agents-envs / gym-unity (Python)
 
 

com.unity.ml-agents/Runtime/Communicator/GrpcExtensions.cs

             ActionSpec actionSpec;
             if (bpp.ActionSpec == null)
             {
+                // Disable deprecation warnings so we can set legacy fields
+#pragma warning disable CS0618
                 var spaceType = (SpaceType)bpp.VectorActionSpaceTypeDeprecated;
                 if (spaceType == SpaceType.Continuous)
                 {
                 {
                     actionSpec = ActionSpec.MakeDiscrete(bpp.VectorActionSizeDeprecated.ToArray());
                 }
+#pragma warning restore CS0618
             }
             else
             {