Fix range of dates.

biscuit/apps/alsijil/views.py

@@ -224,7 +224,7 @@ def manage_absence(request: HttpRequest) -> HttpResponse:
 
             # Mark person as absent
             delta = end_date - start_date
-            for i in range(delta.days+1):
+            for i in range(delta.days):
                 starting_period = starting_lesson if i == 0 else 0
                 day = start_date + timedelta(days=1)
                 person.mark_absent(day, starting_period=starting_period, absent=absent, excused=excused)