don't migrate configurable_from_database setting

lib/mix/tasks/pleroma/config.ex

@@ -76,7 +76,8 @@ defmodule Mix.Tasks.Pleroma.Config do
     group
     |> Application.get_all_env()
     |> Enum.reject(fn {k, _v} ->
-      k in [Pleroma.Repo, :env] or (group == :phoenix and k == :serve_endpoints)
+      k in [Pleroma.Repo, :env, :configurable_from_database] or
+        (group == :phoenix and k == :serve_endpoints)
     end)
     |> Enum.each(fn {key, value} ->
       key = inspect(key)