fix(follow-instances): Show correct error message when trying to follow already following actor

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/graphql/resolvers/admin.ex

@@ -527,6 +527,12 @@ defmodule Mobilizon.GraphQL.Resolvers.Admin do
         Instances.refresh()
         get_instance(parent, args, resolution)
 
+      {:error, :follow_pending} ->
+        {:error, dgettext("errors", "This instance is pending follow approval")}
+
+      {:error, :already_following} ->
+        {:error, dgettext("errors", "You are already following this instance")}
+
       {:error, :http_error} ->
         {:error, dgettext("errors", "Unable to find an instance to follow at this address")}