Backpatch 031_recovery_conflict.pl.

The prior commit showed that the introduction of recovery conflict tests was a
good idea. Without these tests it's hard to know that the fix didn't break
something...

031_recovery_conflict.pl was introduced in 9f8a050f68d and extended in
21e184403bf.

Discussion: https://postgr.es/m/20220413002626.udl7lll7f3o7nre7@alap3.anarazel.de
Backpatch: 10-14