Standardize the way we capture and use Mix.env()

lib/pleroma/uploaders/uploader.ex

@@ -5,6 +5,8 @@
 defmodule Pleroma.Uploaders.Uploader do
   import Pleroma.Web.Gettext
 
+  @mix_env Mix.env()
+
   @moduledoc """
   Defines the contract to put and get an uploaded file to any backend.
   """
@@ -74,7 +76,7 @@ defmodule Pleroma.Uploaders.Uploader do
   end
 
   defp callback_timeout do
-    case Mix.env() do
+    case @mix_env do
       :test -> 1_000
       _ -> 30_000
     end