[Bugfix] Fix day-event fetching

It returned today’s events regardless of the day.

calsocial/calendar_system/gregorian.py

@@ -150,7 +150,7 @@ class GregorianCalendar(CalendarSystem):
         if user:
             events = events.filter(Event.user == user)
 
-        start_timestamp = self.timestamp.replace(hour=0, minute=0, second=0, microsecond=0)
+        start_timestamp = date.replace(hour=0, minute=0, second=0, microsecond=0)
         end_timestamp = start_timestamp + timedelta(days=1)
 
         events = events.filter(((Event.start_time >= start_timestamp) & (Event.start_time < end_timestamp)) |