Make sure to select from selected step

Not clear whether this will actually make a difference, but it seems not
impossible we were selecting from the "parent" collector_progress previously,
which would be wrong.

The intent is that the expected time is updated after a commit is fully
processed, not before; this ensures that we don't jump around as much on the
various print outs of this statistic.

Author: Mark-Simulacrum

database/src/pool/postgres.rs

@@ -429,7 +429,7 @@ impl PostgresConnection {
                         coalesce(end_time, statement_timestamp()) - start_time)::int4,
                     extract(
                         epoch from interval '0 seconds'::interval +
-                        (select end_time - start_time
+                        (select cp.end_time - cp.start_time
                         from collector_progress as cp
                             where
                                 cp.aid != $1