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(at)163(dot)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