docs: Improve log_line_prefix session_id query

doc/src/sgml/config.sgml

@@ -4096,7 +4096,7 @@ local0.*    /var/log/postgresql
          identifier from <literal>pg_stat_activity</>, use this query:
 <programlisting>
 SELECT to_hex(EXTRACT(EPOCH FROM backend_start)::integer) || '.' ||
-       regexp_replace('0000' || to_hex(pid), '^0*(.*....)$', '\1')
+       regexp_replace('0000' || '0133e3', '^0*(.{4,})$', '\1')
 FROM pg_stat_activity;
 </programlisting>