pgsql: Run regression tests with timezone America/Los_Angeles.

Run regression tests with timezone America/Los_Angeles.

Historically we've used timezone "PST8PDT", but the recent release
2024b of tzdb changes the definition of that zone in a way that
breaks many test cases concerned with dates before 1970. Although
we've not yet adopted 2024b into our own tree, this is already
problematic for people using --with-system-tzdata if their platform
has already adopted 2024b. To work with both older and newer
versions of tzdb, switch to using "America/Los_Angeles", accepting
the ensuing changes in regression test results.

Back-patch to all supported branches.

Per report and patch from Wolfgang Walther.

Discussion: https://postgr.es/m/0a997455-5aba-4cf2-a354-d26d8bcbfae6@technowledgy.de

Branch
------
REL_15_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/2b94ee58bf256e1b4682f21f13d0f2c73e1b0cc2

Modified Files
--------------
doc/src/sgml/ref/set.sgml | 4 +-
doc/src/sgml/regress.sgml | 6 +-
src/test/regress/expected/date.out | 10 +--
src/test/regress/expected/horology.out | 57 +++++++------
src/test/regress/expected/timestamptz.out | 137 ++++++++++++++++--------------
src/test/regress/pg_regress.c | 2 +-
src/test/regress/sql/horology.sql | 4 +-
src/test/regress/sql/timestamptz.sql | 5 +-
8 files changed, 120 insertions(+), 105 deletions(-)