Bug in holidays.find_nth_weekday_date() causing invalid holiday dates

[joelonsql]

holidays=# select * from holidays.denmark(2020,2021) where reference = 'Palm Sunday';
datestamp | reference | description | authority | day_off | observation_shifted | start_time | end_time
------------+-------------+-------------+-----------+---------+---------------------+------------+----------
2020-03-29 | Palm Sunday | Palmesøndag | national | t | f | 00:00:00 | 24:00:00
2021-03-21 | Palm Sunday | Palmesøndag | national | t | f | 00:00:00 | 24:00:00
(2 rows)

According to [1], "Palm Sunday" for 2020 is 2020-04-05.
According to Google "Palm Sunday Denmark", the date for 2021 is 2021-03-28.

[1] https://www.oresunddirekt.se/en/working-in-denmark/working-in-denmark/public-holidays-2020-in-sweden-and-denmark