views/week-header: Use minute granurality

We end up losing minutes information when running through this code
path. Technically it's fine, because we copy the minutes from the
event, but it's better nonetheless to operate on the level of
granularity that Calendar supports.

src/gui/views/gcal-week-header.c

@@ -1211,9 +1211,9 @@ move_event_to_cell (GcalWeekHeader        *self,
   dnd_date = g_date_time_add_days (tmp_dt, cell);
 
   /* End date */
-  difference = g_date_time_difference (end_date, start_date) / G_TIME_SPAN_HOUR;
+  difference = g_date_time_difference (end_date, start_date) / G_TIME_SPAN_MINUTE;
 
-  new_end = g_date_time_add_hours (dnd_date, difference);
+  new_end = g_date_time_add_minutes (dnd_date, difference);
   gcal_event_set_date_end (changed_event, new_end);
 
   /*