Restore outer attempt condition when fetching jobs

In some situations a condition to ensure the attempts don't exceed max
attempts is still necessary. By checking the attempts outside the CTE we
maintain optimal query performance for the large scan that finds jobs,
and only apply the check in the small _outer_ query.

lib/oban/engines/basic.ex

@@ -106,6 +106,7 @@ defmodule Oban.Engines.Basic do
       |> with_cte("subset", as: ^subset_query)
       |> join(:inner, [j], x in fragment(~s("subset")), on: true)
       |> where([j, x], j.id == x.id)
+      |> where([j, _], j.attempt < j.max_attempts)
       |> select([j, _], j)
 
     updates = [