Adapt pg_upgrade test to pg_lsn output format difference

Commit 2633dae2e4 added some zero padding to various LSNs output
routines so that the low word is always 8 hex digits long, for easy
human consumption.  This included the pg_lsn datatype, which breaks the
pg_upgrade test when it compares the pg_dump output of an older version.
Silence this problem by setting the pg_lsn columns to NULL before the
upgrade.

Discussion: https://postgr.es/m/202507071504.xm2r26u7lmzr@alvherre.pgsql

src/test/perl/PostgreSQL/Test/AdjustUpgrade.pm

@@ -251,6 +251,32 @@ sub adjust_database_contents
 			'drop operator if exists public.=> (bigint, NONE)');
 	}
 
+	# Version 19 changed the output format of pg_lsn.  To avoid output
+	# differences, set all pg_lsn columns to NULL if the old version is
+	# older than 19.
+	if ($old_version < 19)
+	{
+		if ($old_version >= '9.5')
+		{
+			_add_st($result, 'regression',
+				"update brintest set lsncol = NULL");
+		}
+
+		if ($old_version >= 12)
+		{
+			_add_st($result, 'regression',
+				"update tab_core_types set pg_lsn = NULL");
+		}
+
+		if ($old_version >= 14)
+		{
+			_add_st($result, 'regression',
+				"update brintest_multi set lsncol = NULL");
+			_add_st($result, 'regression',
+				"update brintest_bloom set lsncol = NULL");
+		}
+	}
+
 	return $result;
 }