Add curly brackets to mutation example for TS

Adding curly brackets to arrow function which "disables" the implicit return value for TypeScript users.

Author: bennettdams

docs/src/pages/guides/updates-from-mutation-responses.md

@@ -9,7 +9,9 @@ When dealing with mutations that **update** objects on the server, it's common f
 const queryClient = useQueryClient()
 
 const mutation = useMutation(editTodo, {
-  onSuccess: data => queryClient.setQueryData(['todo', { id: 5 }], data),
+  onSuccess: data => {
+    queryClient.setQueryData(['todo', { id: 5 }], data)
+  }
 })
 
 mutation.mutate({