* When before_compile callback injects the two
__set_new_state__ functions being one of them
with a guard clause checking if the `new_state` is
a function

```elixir
defp __set_new_state__(resource, new_state) when is_function(new_state) do
  new_state.(resource)
end

defp __set_new_state__(_, new_state), do: new_state
```

and the transitions defined in the module using machinist has all `to: state` definitions being a string, the `__set_new_state__/2 when is_function/1` will never be used. That’s why dialyzer reports the following warning:

```
The guard test:

is_function(_ :: <<_::64, _::size(8)>>)

can never succeed.
```

Fix dialyzer warning of __set_new_state__ private function