Drop invalid indexes concurrently when reindexing

The `DROP INDEX` query would lock the whole table with an `ACCESS
EXCLUSIVE` lock and could cause queries to fail unexpectedly.

Closes #1247

Author: sorentwo

lib/oban/plugins/reindexer.ex

@@ -154,7 +154,7 @@ defmodule Oban.Plugins.Reindexer do
           AND NOT indisvalid
           AND starts_with(relname, 'oban_jobs')
       LOOP
-        EXECUTE format('DROP INDEX %s.%s', rec.namespace, rec.relname);
+        EXECUTE format('DROP INDEX CONCURRENTLY %s.%s', rec.namespace, rec.relname);
       END LOOP;
     END $$
     """