instance.gen task: Only show files which will be actually overwritten

lib/mix/tasks/pleroma/instance.ex

@@ -253,7 +253,7 @@ def run(["gen" | rest]) do
     else
       shell_error(
         "The task would have overwritten the following files:\n" <>
-          (Enum.map(paths, &"- #{&1}\n") |> Enum.join("")) <>
+          (Enum.map(will_overwrite, &"- #{&1}\n") |> Enum.join("")) <>
           "Rerun with `--force` to overwrite them."
       )
     end