Use a more portable way to get the version string in PostgresNode

Older versions of perl on Windows don't like the list form of pipe open,
and perlcritic doesn't like the string form of open, so we avoid both
with a simpler formulation using qx{}.

Per complaint from Amit Kapila.

src/test/perl/PostgresNode.pm

@@ -1248,10 +1248,8 @@ sub _set_pg_version
 	local %ENV = $self->_get_env();
 
 	# We only want the version field
-	open my $fh, "-|", $pg_config, "--version"
-	  or BAIL_OUT("$pg_config failed: $!");
-	my $version_line = <$fh>;
-	close $fh or die;
+	my $version_line = qx{$pg_config --version};
+	BAIL_OUT("$pg_config failed: $!") if $?;
 
 	$self->{_pg_version} = PostgresVersion->new($version_line);