Fix timing issue in deadlock recovery conflict test.

Per buildfarm members longfin and skink.

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

Author: anarazel

src/test/recovery/t/031_recovery_conflict.pl

@@ -231,6 +231,14 @@
 $sect = "startup deadlock";
 $expected_conflicts++;
 
+# Want to test recovery deadlock conflicts, not buffer pin conflicts. Without
+# changing max_standby_streaming_delay it'd be timing dependent what we hit
+# first
+$node_standby->adjust_conf('postgresql.conf', 'max_standby_streaming_delay',
+						   "${PostgreSQL::Test::Utils::timeout_default}s");
+$node_standby->restart();
+reconnect_and_clear();
+
 # Generate a few dead rows, to later be cleaned up by vacuum. Then acquire a
 # lock on another relation in a prepared xact, so it's held continuously by
 # the startup process. The standby psql will block acquiring that lock while
@@ -286,6 +294,9 @@
 
 # clean up for next tests
 $node_primary->safe_psql($test_db, qq[ROLLBACK PREPARED 'lock';]);
+$node_standby->adjust_conf('postgresql.conf', 'max_standby_streaming_delay', '50ms');
+$node_standby->restart();
+reconnect_and_clear();
 
 
 # Check that expected number of conflicts show in pg_stat_database. Needs to