In 002_blocks.pl, try to prevent a HOT update.

Make the new tuple larger than the old one so that it, hopefully, won't
manage to squeeze into leftover freespace on the same page. The test
is trying to verify that the UPDATE touches 2 pages, but if a HOT
update happens, then it doesn't.

Per buildfarm.

src/bin/pg_walsummary/t/002_blocks.pl

@@ -56,7 +56,8 @@ note_wal_summary_dir("after insert", $node1);
 
 # Update a row in the first block of the table and trigger a checkpoint.
 $node1->safe_psql('postgres', <<EOM);
-UPDATE mytable SET b = 'abcdefghijklmnopqrstuvwxyz' WHERE a = 2;
+UPDATE mytable SET b = 'abcdefghijklmnopqrstuvwxyz' || b || '01234567890'
+	WHERE a = 2;
 CHECKPOINT;
 EOM