Fix 004_subscription.pl to allow its usage in --link mode.

Fix 004_subscription.pl to allow its usage in --link mode.

The test was failing when executed in --link mode and the reason was that
we were using the old cluster from a previously successful upgrade test.
Re-arrange the tests so that the successful test case is at the end.

Reported-by: Justin Pryzby, Peter Eisentraut
Author: Kuroda Hayato
Reviewed-by: Vignesh C, Amit Kapila
Discussion: https://postgr.es/m/ZcvZipRoi_kopIpb@pryzbyj2023
Discussion: https://postgr.es/m/25f7f4bf-9e75-4453-b666-7818000cefe6@eisentraut.org