Check again whether holidays are really in the exdates

also consider that validity ranges have to resynced if they are affected by holiday changes.

assigned to @hansegucker

added part::backend type::bug labels

assigned to @hansegucker

moved from AlekSIS/official/AlekSIS-App-Chronos#235 (moved)

changed the description

Blocked by !23 (merged)

added workflow::blocked label

Also show holidays in timetables

mentioned in merge request AlekSIS/official/AlekSIS-App-Chronos!355 (merged)

mentioned in merge request AlekSIS/official/AlekSIS-Core!1520 (merged)

closed