Fix build

Author: JamesNK

src/Grpc/JsonTranscoding/src/Shared/Server/UnaryServerMethodInvoker.cs

@@ -159,7 +159,7 @@ private async Task<TResponse> AwaitInvoker(Task<TResponse> invokerTask, GrpcActi
         }
     }
 
-    private async Task<TResponse> AwaitServiceReleaseAndThrow(ValueTask releaseTask, ExceptionDispatchInfo ex)
+    private static async Task<TResponse> AwaitServiceReleaseAndThrow(ValueTask releaseTask, ExceptionDispatchInfo ex)
     {
         await releaseTask;
         ex.Throw();