Fix aggregation of absences and tardninesses

I added a tardiness of 5 minutes and one absence to one lesson. It was the only lesson the user had at this day.

added type::bug label

changed title from Absence values get multiplied to Fix aggregation of absences and tardninesses

created merge request !52 (merged) to address this issue

mentioned in merge request !52 (merged)

closed via commit c83ec781

closed via merge request !52 (merged)

mentioned in commit c83ec781