BUG #19367: typos in backend/utils/adt/timestamp.c

The following bug has been logged on the website:

Bug reference:      19367
Logged by:          Nikolay Fadeev
Email address:      fadeymail@rambler.ru
PostgreSQL version: 18.1
Operating system:   all OS
Description:

There are typos in return type of these functions:
1) timestamptz_pl_interval_at_zone(PG_FUNCTION_ARGS)
    NOW: PG_RETURN_TIMESTAMP(timestamptz_pl_interval_internal(timestamp,
span, attimezone));
    SHOULD:
PG_RETURN_TIMESTAMPTZ(timestamptz_pl_interval_internal(timestamp, span,
attimezone));
2) Datum timestamptz_mi_interval_at_zone(PG_FUNCTION_ARGS)
    NOW: PG_RETURN_TIMESTAMP(timestamptz_mi_interval_internal(timestamp,
span, attimezone));
    SHOULD:
PG_RETURN_TIMESTAMPTZ(timestamptz_mi_interval_internal(timestamp, span,
attimezone));