Fix buildfarm error from commit 5c31669058.

Skip test when not using unix domain sockets.

Discussion: https://postgr.es/m/CALDaNm29-8OozsBWo9H6DN_Tb_3yA1QjRJput-KhaN8ncDJtJA@mail.gmail.com
Backpatch-through: 16

src/test/subscription/t/027_nosuperuser.pl

@@ -5,6 +5,7 @@
 use strict;
 use warnings;
 use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
 use Test::More;
 
 my ($node_publisher, $node_subscriber, $publisher_connstr, $result, $offset);
@@ -306,7 +307,12 @@ expect_replication("alice.unpartitioned", 3, 17, 21,
 # If the subscription connection requires a password ('password_required'
 # is true) then a non-superuser must specify that password in the connection
 # string.
-$ENV{"PGPASSWORD"} = 'secret';
+SKIP:
+{
+	skip
+	  "subscription password_required test cannot run without Unix-domain sockets",
+	  3
+	  unless $use_unix_sockets;
 
 	my $node_publisher1 = PostgreSQL::Test::Cluster->new('publisher1');
 	my $node_subscriber1 = PostgreSQL::Test::Cluster->new('subscriber1');
@@ -344,6 +350,9 @@ CREATE SUBSCRIPTION regress_test_sub CONNECTION '$publisher_connstr1' PUBLICATIO
 	$node_subscriber1->wait_for_subscription_sync($node_publisher1,
 		'regress_test_sub');
 
+	my $save_pgpassword = $ENV{"PGPASSWORD"};
+	$ENV{"PGPASSWORD"} = 'secret';
+
 	# Setup pg_hba configuration so that logical replication connection without
 	# password is not allowed.
 	unlink($node_publisher1->data_dir . '/pg_hba.conf');
@@ -366,11 +375,12 @@ ALTER SUBSCRIPTION regress_test_sub REFRESH PUBLICATION;
 	isnt($ret, 0,
 		"non zero exit for subscription whose owner is a non-superuser must specify password parameter of the connection string"
 	);
-ok( $stderr =~ m/DETAIL:  Non-superusers must provide a password in the connection string./,
+	ok( $stderr =~
+		  m/DETAIL:  Non-superusers must provide a password in the connection string./,
 		'subscription whose owner is a non-superuser must specify password parameter of the connection string'
 	);
 
-delete $ENV{"PGPASSWORD"};
+	$ENV{"PGPASSWORD"} = $save_pgpassword;
 
 	# It should succeed after including the password parameter of the connection
 	# string.
@@ -383,4 +393,5 @@ ALTER SUBSCRIPTION regress_test_sub REFRESH PUBLICATION;
 	is($ret, 0,
 		"Non-superuser will be able to refresh the publication after specifying the password parameter of the connection string"
 	);
+}
 done_testing();