fix F# testing

testing-unit-fs-mocks/Testing.fs

@@ -12,7 +12,7 @@
     interface IMocks with
         member this.NewResourceAsync(args: MockResourceArgs): Task<ValueTuple<string,obj>> =
             let inputKVs = args.Inputs |> Seq.map(fun kv -> kv.Key, kv.Value) |> Seq.toList
             let nameKVs = if args.Inputs.ContainsKey("name") then [] else [("name", args.Name :> obj)]
             let endpointKVs =
                 if args.Type = "azure:storage/account:Account"
                 then ["primaryWebEndpoint", sprintf "https://%s.web.core.windows.net" args.Name :> obj]
@@ -26,10 +26,10 @@
             let dict = outputs.ToImmutableDictionary() :> obj            
 
             // Default the resource ID to `{name}_id`.
             let id = if args.Id = null then sprintf "%s_id" args.Name else args.Id 
             Task.FromResult(struct (id, dict))
 
         member this.CallAsync(args: MockCallArgs): Task<obj> =
             // We don't use this method in this particular test suite.
             // Default to returning whatever we got as input.
-            Task.FromResult(null :> obj)
+            Task.FromResult(null)