Fix contrib/pageinspect's test for sequences.

I managed to break this test in two different ways in commit
05036a3.

First, the output of the new call to tuple_data_split() on the test
sequence is dependent on endianness.  This is fixed by setting a
special start value for the test sequence that produces the same
output regardless of the endianness of the machine.

Second, on versions older than v15, the new test case fails under
"force_parallel_mode = regress" with the following error:

	ERROR:  cannot access temporary tables during a parallel operation

This is because pageinspect's disk-accessing functions are
incorrectly marked PARALLEL SAFE on versions older than v15 (see
commit aeaaf52 for details).  This one is fixed by changing the
test sequence to be permanent.  The only reason it was previously
marked temporary was to avoid needing a DROP SEQUENCE command at
the end of the test.  Unlike some other tests in this file, the use
of a permanent sequence here shouldn't result in any test
instability like what was fixed by commit e2933a6.

Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/ZuOKOut5hhDlf_bP%40nathan
Backpatch-through: 12

Author: nathan-bossart

contrib/pageinspect/expected/page.out

@@ -240,11 +240,12 @@ SELECT page_checksum(decode(repeat('00', :block_size), 'hex'), 1);
 (1 row)
 
 -- tests for sequences
-create temporary sequence test_sequence;
+create sequence test_sequence start 72057594037927937;
 select tuple_data_split('test_sequence'::regclass, t_data, t_infomask, t_infomask2, t_bits)
   from heap_page_items(get_raw_page('test_sequence', 0));
                    tuple_data_split                    
 -------------------------------------------------------
- {"\\x0100000000000000","\\x0000000000000000","\\x00"}
+ {"\\x0100000000000001","\\x0000000000000000","\\x00"}
 (1 row)
 
+drop sequence test_sequence;

contrib/pageinspect/sql/page.sql

@@ -100,6 +100,7 @@ SELECT page_header(decode(repeat('00', :block_size), 'hex'));
 SELECT page_checksum(decode(repeat('00', :block_size), 'hex'), 1);
 
 -- tests for sequences
-create temporary sequence test_sequence;
+create sequence test_sequence start 72057594037927937;
 select tuple_data_split('test_sequence'::regclass, t_data, t_infomask, t_infomask2, t_bits)
   from heap_page_items(get_raw_page('test_sequence', 0));
+drop sequence test_sequence;