Disable 031_recovery_conflict.pl until after minor releases.

f40d362a66 disabled part of 031_recovery_conflict.pl due to instability
that's not trivial to fix in the back branches. That fixed most of the
issues. But there was one more failure (on lapwing / REL_10_STABLE).

That failure looks like it might be caused by a genuine problem. Disable the
test until after the set of releases, to avoid packagers etc potentially
having to fight with a test failure they can't do anything about.

Discussion: https://postgr.es/m/3447060.1652032749@sss.pgh.pa.us
Backpatch: 10-14

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

@@ -10,6 +10,7 @@ use PostgreSQL::Test::Cluster;
 use PostgreSQL::Test::Utils;
 use Test::More;
 
+plan skip_all => "disabled until after minor releases, due to instability";
 
 # Set up nodes
 my $node_primary = PostgreSQL::Test::Cluster->new('primary');