Warn users about non-ghcup channels

Author: qxrein

lib/GHCup/Download.hs

@@ -89,6 +89,8 @@ import qualified Data.Text                     as T
 import qualified Data.Text.IO                  as T
 import qualified Data.Text.Encoding            as E
 import qualified Data.Yaml.Aeson               as Y
+import Data.List (isPrefixOf)
+import Control.Monad.IO.Class (liftIO)
 
 
 
@@ -890,4 +892,4 @@ applyMirrors (DM ms) uri@(URI { uriAuthority = Just (Authority { authorityHost =
           }
     Just (DownloadMirror auth Nothing) ->
       uri { uriAuthority = Just auth }
-applyMirrors _ uri = uri
+applyMirrors _ uri = uri