Add changelog file

ee/changelogs/322079-allow-overnight-oncall-shifts.yml

+---
+title: Allow overnight shifts for oncall rotations
+merge_request: 57202
+author:
+type: added

ee/lib/incident_management/oncall_shift_generator.rb

@@ -129,15 +129,10 @@ module IncidentManagement
           #     expected_shift_count = 14          -> pretend it's a 2-week rotation
           #     shift_count = 2                    -> we're calculating the shift for the 3rd day
           # starts_at = Monday 00:00:00 + 8.hours + 2.days => Thursday 08:00:00
-          start_date = shift_cycle_starts_at + shift_count.days
+          start_date = end_date = shift_cycle_starts_at + shift_count.days
+          end_date = start_date + 1.day unless rotation.active_period.end_after_start?
 
-          shift_start_date, shift_end_date = if rotation.active_period.end_after_start?
-                                               [start_date, start_date]
-                                             else
-                                               [start_date, start_date + 1.day]
-                                             end
-
-          starts_at, ends_at = rotation.active_period.for_dates(shift_start_date, shift_end_date)
+          starts_at, ends_at = rotation.active_period.for_dates(start_date, end_date)
 
           shift_for(participant, [rotation.starts_at, starts_at].max, limit_end_time(ends_at))
         end