BUG #17366: Error result returned in timestamp2timestamptz, expected to be off by one hour

The following bug has been logged on the website:

Bug reference:      17366
Logged by:          Error result returned in timestamp2timestamptz, expected to be off by one
hour
Email address:      dafoer_x@163.com
PostgreSQL version: 14.1
Operating system:   REL_14_STABLE
Description:

For REL_14_STABLE
git log ad5b6f248ab288c3252d8122d12a1eb410d4a0b6

e.g.
postgres=# set timezone to "PST8PDT";
SET
postgres=# select * from pg_timezone_names where name = 'PST8PDT';
  name   | abbrev | utc_offset | is_dst 
---------+--------+------------+--------
 PST8PDT | PST    | -08:00:00  | f
(1 row)

postgres=# select (timestamp '2021-03-14 02:00:00')::timestamptz;
      timestamptz       
------------------------
 2021-03-14 03:00:00-07
(1 row)

postgres=# select (timestamp '2021-03-14 03:00:00')::timestamptz;
      timestamptz       
------------------------
 2021-03-14 03:00:00-07
(1 row)


expected:
postgres=# select (timestamp '2021-03-14 02:00:00')::timestamptz;
2021-03-14 02:00:00-07